drm/xe: add some debug info for d3cold

From the CI logs we want to easily know if the machine is capable and
allowed to enter d3cold, and can therefore potentially trigger the
d3cold RPM suspend and resume path.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>