drivers: gpio: silabs: add lookup table documentation

[Martinhoff-maker]

This commit only adds documentation. It will help a user to translate pinout from the reference manual to a device tree gpio (HP and ULP).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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[jhedberg]

I guess this wont get generated to any html and be available e.g. on docs.zephyrproject.org? I suppose it might make sense to have this in some rst file too?

[Martinhoff-maker]

I agree with you Johan, but I haven't found the right spot to put this. Since GPIO port and pin are defined at the SoC level, I would like to put it here, but there is no documentation at the SoC level. The only place where I could put this is in the board documentation, but it would be duplicated for each board that uses the SiWx917 SoC.

[jhedberg]

I agree with you Johan, but I haven't found the right spot to put this. Since GPIO port and pin are defined at the SoC level, I would like to put it here, but there is no documentation at the SoC level. The only place where I could put this is in the board documentation, but it would be duplicated for each board that uses the SiWx917 SoC.

Probably out of scope for this PR, but we should either refactor the Silabs board documentation so that we can have shared rst files for each board that use the same SoC, or then introduce a standard way and location to provide SoC-level documentation. @kartben is there any guidance wrt this?