drm/xe/display: move compat runtime pm stubs to the correct file

Move things that belong to intel_runtime_pm.h to the correct place. Add
missing header guards while at it.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/edefb6ef02920528eacdf01b828cfc45ce55e061.1717004739.git.jani.nikula@intel.com