arch: arm: refactor pm_s2ram

What is the change?
 - APIs `pm_s2ram_mark_set` and `pm_s2ram_mark_check_and_clear`,
   used to set/check pm_s2ram magic marker,
   no longer have Arm specific limitations.

Why is this needed?
 - These APIs are generic and should not have arch specific dependency.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>