boards: silabs: Use DBUS pinctrl driver for Series 2 boards

Swap from silabs,gecko-pinctrl to silabs,dbus-pinctrl for all boards
with Series 2 SoCs. Explicitly declare pin properties as part of
pinctrl pinout configuration.

Signed-off-by: Aksel Skauge Mellbye <aksel.mellbye@silabs.com>