add "Series 3" (SiMG301 SiBG301 SixG301) SoC support

Hello, greetings.

I'd like to see Zephyr support for the [Series 3 SoC]( 
https://news.silabs.com/2025-10-02-Silicon-Labs-Series-3-SoCs-Now-Available-to-Power-the-Next-Era-of-Connectivity). I'm opening this issue so folks have something to follow. Awaiting with great excitement over here; congrats on the awesome chip all.