drm/xe: Make the gem shrinker drm managed

Make the xe drm shrinker drm managed like many other resources
created at device creation time.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250508113015.3374-1-thomas.hellstrom@linux.intel.com