drm/xe: Only init runtime PM after all d3cold config is in place.

We cannot allow runtime pm suspend after we configured the
d3cold capable and threshold.

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