ext: gecko: Add Silabs Gecko SDK for EFM32TG SoCs

[LukasWoodtli]

Origin: Silicon Labs Gecko SDK
URL: https://github.com/SiliconLabs/Gecko_SDK
Version: v4.4.6 (SHA: 59d2160fe448b13730a91c0f019a8b4c53c43eb2)
Purpose: Add support for Silicon Labs EXX32 SoCs
License: Zlib
Maintained-by: External

[LukasWoodtli]

Needed for PR boards: silabs: Support for efm32tg_stk3300

[asmellby]

The startup_* files are not needed in Zephyr, since Zephyr has its own way of refining the vector table and reset handler (see prep_c.c).

These files are also ineligible for inclusion in Zephyr due to the license header (for some reason) declaring the MSLA license, which is not an OSI approved open source license.

The combination of these two factors means that you can safely (and must) drop the startup_* files from this PR.

[jerome-pouiller]

I only have some comments about the commit message.

These days, the usual prefix for this kind of changes is gecko: (rather than ext: gecko: ).

Can you add the field commit: (as in the example here) (otherwise, it is not clear you are talking about the sha of the commit or of the files).

I also suggest to change Add support for Silicon Labs EXX32 SoCs in Add support for Silicon Labs EFM32TG SoCs.

[asmellby]

You will probably need to rebase this in order for CI to pass in the main tree, due to the addition of support for other devices.

[LukasWoodtli]

Can this be merged?

[jhedberg]

@LukasWoodtli the main tree PR (zephyrproject-rtos/zephyr#91191) should be passing CI before we merge this (besides a manifest check failure as long as it's referencing this PR). You should also take it away from being a Draft.