dts: pinctrl: add mspm0gx51x support and common-base G-series pinctrl

[Girinandha-M]

Add pinctrl for MSPM0G gx51x family (G151x/G351x) and extract
nodes shared across all G-series families into a common file.

286 identical nodes moved to mspm0g-common-pinctrl.dtsi.
129 conflict nodes (same pin, different mux values) remain in
per-family delta files. All mux values cross-checked against
SDK device headers (1664/1664 passed).

Tested on LP_MSPM0G3507 and LP_MSPM0G3519 with GPIO, UART,
CANFD, PWM, ADC, DAC, VREF, and SPI samples.

[ssekar15]

@JFMSP based on your PR #83.

[JFMSP]

@ssekar15 and @Girinandha-M These devices for mspm0g are not designed to continue to share a commonality in pinctrl long term nor are easily scalable. For maintainability I think it is a better practice to keep the device families separate and allow each file to be determined specifically by that devices pin control information. Adding future MSPM0G devices such as MSPM0G5187 will further complicate the base file and require consistent refactor across all current MSPM0G files

I strongly recommend against the creation of a base file.

[ssekar15]

@ssekar15 and @Girinandha-M These devices for mspm0g are not designed to continue to share a commonality in pinctrl long term nor are easily scalable. For maintainability I think it is a better practice to keep the device families separate and allow each file to be determined specifically by that devices pin control information. Adding future MSPM0G devices such as MSPM0G5187 will further complicate the base file and require consistent refactor across all current MSPM0G files

I strongly recommend against the creation of a base file.

I understand your concern we should avoid a 'one-size-fits-all' file. The logic is the standard programming principle of reusable APIs: if multiple SoCs share identical pinctrl logic, we should centralize to prevent duplication and maintenance errors.
If a future device like the MSPM0G5187 is fundamentally different, it simply wouldn't inherit the base file. if a new set of devices compatible, we create a 'Base V2' for new group.

[JFMSP]

@ssekar15 and @Girinandha-M These devices for mspm0g are not designed to continue to share a commonality in pinctrl long term nor are easily scalable. For maintainability I think it is a better practice to keep the device families separate and allow each file to be determined specifically by that devices pin control information. Adding future MSPM0G devices such as MSPM0G5187 will further complicate the base file and require consistent refactor across all current MSPM0G files
I strongly recommend against the creation of a base file.

I understand your concern we should avoid a 'one-size-fits-all' file. The logic is the standard programming principle of reusable APIs: if multiple SoCs share identical pinctrl logic, we should centralize to prevent duplication and maintenance errors. If a future device like the MSPM0G5187 is fundamentally different, it simply wouldn't inherit the base file. if a new set of devices compatible, we create a 'Base V2' for new group.

The worry here for me is that we'll end up having a V3, V4, and so on as additional devices get added, and we can avoid the headache, and the savings from this long term I think will start to be outweighed by the headache of maintaining a common file.