soc: nordic: nrf54h: poweroff: Add support for s2ram

Add functions for local domain suspend to RAM. Add matching resume
procedure. Add pm_s2ram function for determining source of reset.
Add preserving NVIC and MPU state in retained RAM when CPU is powered off
during S2RAM procedure.

Signed-off-by: Adam Kondraciuk <adam.kondraciuk@nordicsemi.no>