=========
It appears that the only usage of am33xx-l4.dtsi is for am335x for which
specific parts mentioned in those dtsi files are 3352, 3358, and 3359.

$ git grep am33xx-l4.dtsi
arch/arm/boot/dts/am33xx.dtsi:#include "am33xx-l4.dtsi"
$ git grep -l '#include "am33xx.dtsi"' arch/ |wc -l
27
$ git grep -l '#include "am33xx.dtsi"' arch/ |grep -v am335x |wc -l
0

The only TI AM33xx parts that actually exist are:
AM3351, AM3352, AM3354, AM3356, AM3357, AM3358, AM3359

I've been told by a TI engineer that there may have been plans for more
AM3xxx parts but only AM335x was ever brought to market.

I clicked on the datasheet link for each product page and while the URL
has the specific part number in it [0], they all end up loading the
exact same PDF. The header states:

"AM3359, AM3358, AM3357, AM3356, AM3354, AM3352, AM3351
SPRS717L – OCTOBER 2011 – REVISED MARCH 2020"

Thus, I do believe all SoC's using am33xx-l4.dtsi would have the same
memory map for the pin control registers and the same relationship from
pin to gpio line.  For example, GPMC_A0 has mode 7 and it is labeled
gpio1_16.  conf_gpmc_a0 is at offset 840h which makes it pin 16.

Maybe am33xx-l4.dtsi should have actually been named am335x-l4.dtsi?

Though I suppose there is no point in changing that now.

[0] https://www.ti.com/lit/ds/symlink/am3359.pdf


V1 notes:
=========
There was previous dicussion relevant to this patch:
https://lore.kernel.org/linux-gpio/20200525131731.GA948395@x1/

Here is the list I compiled which shows the mapping between a gpioline
and the pin number including the memory address for the pin control
register

gpiochip,gpio-line,pinctrl-PIN,pinctrl-address
0,0,82,44e10948
0,1,83,44e1094c
0,2,84,44e10950
0,3,85,44e10954
0,4,86,44e10958
0,5,87,44e1095c
0,6,88,44e10960
0,7,89,44e10964
0,8,52,44e108d0
0,9,53,44e108d4
0,10,54,44e108d8
0,11,55,44e108dc
0,12,94,44e10978
0,13,95,44e1097c
0,14,96,44e10980
0,15,97,44e10984
0,16,71,44e1091c
0,17,72,44e10920
0,18,135,44e10a1c
0,19,108,44e109b0
0,20,109,44e109b4
0,21,73,44e10924
0,22,8,44e10820
0,23,9,44e10824
0,26,10,44e10828
0,27,11,44e1082c
0,28,74,44e10928
0,29,81,44e10944
0,30,28,44e10870
0,31,29,44e10874
1,0,0,44e10800
1,1,1,44e10804
1,2,2,44e10808
1,3,3,44e1080c
1,4,4,44e10810
1,5,5,44e10814
1,6,6,44e10818
1,7,7,44e1081c
1,8,90,44e10968
1,9,91,44e1096c
1,10,92,44e10970
1,11,93,44e10974
1,12,12,44e10830
1,13,13,44e10834
1,14,14,44e10838
1,15,15,44e1083c
1,16,16,44e10840
1,17,17,44e10844
1,18,18,44e10848
1,19,19,44e1084c
1,20,20,44e10850
1,21,21,44e10854
1,22,22,44e10858
1,23,23,44e1085c
1,24,24,44e10860
1,25,25,44e10864
1,26,26,44e10868
1,27,27,44e1086c
1,28,30,44e10878
1,29,31,44e1087c
1,30,32,44e10880
1,31,33,44e10884
2,0,34,44e10888
2,1,35,44e1088c
2,2,36,44e10890
2,3,37,44e10894
2,4,38,44e10898
2,5,39,44e1089c
2,6,40,44e108a0
2,7,41,44e108a4
2,8,42,44e108a8
2,9,43,44e108ac
2,10,44,44e108b0
2,11,45,44e108b4
2,12,46,44e108b8
2,13,47,44e108bc
2,14,48,44e108c0
2,15,49,44e108c4
2,16,50,44e108c8
2,17,51,44e108cc
2,18,77,44e10934
2,19,78,44e10938
2,20,79,44e1093c
2,21,80,44e10940
2,22,56,44e108e0
2,23,57,44e108e4
2,24,58,44e108e8
2,25,59,44e108ec
2,26,60,44e108f0
2,27,61,44e108f4
2,28,62,44e108f8
2,29,63,44e108fc
2,30,64,44e10900
2,31,65,44e10904
3,0,66,44e10908
3,1,67,44e1090c
3,2,68,44e10910
3,3,69,44e10914
3,4,70,44e10918
3,5,98,44e10988
3,6,99,44e1098c
3,9,75,44e1092c
3,10,76,44e10930
3,13,141,44e10a34
3,14,100,44e10990
3,15,101,44e10994
3,16,102,44e10998
3,17,103,44e1099c
3,18,104,44e109a0
3,19,105,44e109a4
3,20,106,44e109a8
3,21,107,44e109ac

On a BeagleBlack Black board (AM3358) with this patch:
cat /sys/kernel/debug/pinctrl/44e10800.pinmux-pinctrl-single/gpio-ranges

GPIO ranges handled:
0: gpio-0-31 GPIOS [0 - 7] PINS [82 - 89]
8: gpio-0-31 GPIOS [8 - 11] PINS [52 - 55]
12: gpio-0-31 GPIOS [12 - 15] PINS [94 - 97]
16: gpio-0-31 GPIOS [16 - 17] PINS [71 - 72]
18: gpio-0-31 GPIOS [18 - 18] PINS [135 - 135]
19: gpio-0-31 GPIOS [19 - 20] PINS [108 - 109]
21: gpio-0-31 GPIOS [21 - 21] PINS [73 - 73]
22: gpio-0-31 GPIOS [22 - 23] PINS [8 - 9]
26: gpio-0-31 GPIOS [26 - 27] PINS [10 - 11]
28: gpio-0-31 GPIOS [28 - 28] PINS [74 - 74]
29: gpio-0-31 GPIOS [29 - 29] PINS [81 - 81]
30: gpio-0-31 GPIOS [30 - 31] PINS [28 - 29]
0: gpio-32-63 GPIOS [32 - 39] PINS [0 - 7]
8: gpio-32-63 GPIOS [40 - 43] PINS [90 - 93]
12: gpio-32-63 GPIOS [44 - 59] PINS [12 - 27]
28: gpio-32-63 GPIOS [60 - 63] PINS [30 - 33]
0: gpio-64-95 GPIOS [64 - 81] PINS [34 - 51]
18: gpio-64-95 GPIOS [82 - 85] PINS [77 - 80]
22: gpio-64-95 GPIOS [86 - 95] PINS [56 - 65]
0: gpio-96-127 GPIOS [96 - 100] PINS [66 - 70]
5: gpio-96-127 GPIOS [101 - 102] PINS [98 - 99]
7: gpio-96-127 GPIOS [103 - 104] PINS [75 - 76]
13: gpio-96-127 GPIOS [109 - 109] PINS [141 - 141]
14: gpio-96-127 GPIOS [110 - 117] PINS [100 - 107]

 arch/arm/boot/dts/am33xx-l4.dtsi | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/arm/boot/dts/am33xx-l4.dtsi b/arch/arm/boot/dts/am33xx-l4.dtsi
index 5ed7f3c58c0f..340ea331e54d 100644
--- a/arch/arm/boot/dts/am33xx-l4.dtsi
+++ b/arch/arm/boot/dts/am33xx-l4.dtsi
@@ -151,6 +151,18 @@ SYSC_OMAP2_SOFTRESET |
 
 			gpio0: gpio@0 {
 				compatible = "ti,omap4-gpio";
+				gpio-ranges =	<&am33xx_pinmux  0  82 8>,
+						<&am33xx_pinmux  8  52 4>,
+						<&am33xx_pinmux 12  94 4>,
+						<&am33xx_pinmux 16  71 2>,
+						<&am33xx_pinmux 18 135 1>,
+						<&am33xx_pinmux 19 108 2>,
+						<&am33xx_pinmux 21  73 1>,
+						<&am33xx_pinmux 22   8 2>,
+						<&am33xx_pinmux 26  10 2>,
+						<&am33xx_pinmux 28  74 1>,
+						<&am33xx_pinmux 29  81 1>,
+						<&am33xx_pinmux 30  28 2>;
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
@@ -1298,6 +1310,10 @@ SYSC_OMAP2_SOFTRESET |
 
 			gpio1: gpio@0 {
 				compatible = "ti,omap4-gpio";
+				gpio-ranges =   <&am33xx_pinmux  0  0  8>,
+						<&am33xx_pinmux  8 90  4>,
+						<&am33xx_pinmux 12 12 16>,
+						<&am33xx_pinmux 28 30  4>;
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
@@ -1700,6 +1716,9 @@ SYSC_OMAP2_SOFTRESET |
 
 			gpio2: gpio@0 {
 				compatible = "ti,omap4-gpio";
+                                gpio-ranges =	<&am33xx_pinmux  0 34 18>,
+						<&am33xx_pinmux 18 77  4>,
+						<&am33xx_pinmux 22 56 10>;
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
@@ -1733,6 +1752,11 @@ SYSC_OMAP2_SOFTRESET |
 
 			gpio3: gpio@0 {
 				compatible = "ti,omap4-gpio";
+				gpio-ranges =	<&am33xx_pinmux  0  66 5>,
+						<&am33xx_pinmux  5  98 2>,
+						<&am33xx_pinmux  7  75 2>,
+						<&am33xx_pinmux 13 141 1>,
+						<&am33xx_pinmux 14 100 8>;
 				gpio-controller;
 				#gpio-cells = <2>;
 				interrupt-controller;
