drm/xe/xe_sysctrl: Add System Controller power management support

drm/xe/xe_sysctrl: Add System Controller power management support

Add resume handling for System Controller to support system (S3/S4) and
runtime power management transitions.

On resume, restore SoC remapper configuration and mailbox interface to
re‑establish communication with firmware.

Signed-off-by: Anoop Vijay <anoop.c.vijay@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patch.msgid.link/20260327131837.2192929-15-anoop.c.vijay@intel.com