drm/xe: Ensure memory eviction on s2idle.

On discrete cards we cannot allow the pci subsystem to skip
the regular suspend and we need to unblock the d3cold.

Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>