soc: nordic: nrf54h: gpd: yield() to not block if main is coop

The main thread, if configured with coop priority (don't do that :D)
breaks gpd since it has a non yielding while loop (also don't do that)

Add an explicit yield() to allow other threads to run if main or other
threads use gpd with coop prio.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>