drm/xe/xe_sysctrl: Add System Controller initialization support

drm/xe/xe_sysctrl: Add System Controller initialization support

Add initialization and cleanup infrastructure for System Controller
subsystem and integrate it into xe device probe path.

During initialization, platform support is checked via has_sysctrl
capability flag and the mailbox region is configured through SoC
remapper interface.

Signed-off-by: Anoop Vijay <anoop.c.vijay@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patch.msgid.link/20260327131837.2192929-13-anoop.c.vijay@intel.com