drivers: gpio: Introduce support for SiWx91x

Implement GPIO driver for Siliconlab SiWx917 family.

This driver support high Performance (HP), Ultra Low Power (ULP) and
Ultra Ultra Low Power (UULP) GPIOs.

Co-authored-by: Aksel Skauge Mellbye <aksel.mellbye@silabs.com>
Signed-off-by: Aksel Skauge Mellbye <aksel.mellbye@silabs.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>