drm/xe: Allow the pm notifier to continue on failure

drm/xe: Allow the pm notifier to continue on failure

Its actions are opportunistic anyway and will be completed
on device suspend.

Marking as a fix to simplify backporting of the fix
that follows in the series.

v2:
- Keep the runtime pm reference over suspend / hibernate and
  document why. (Matt Auld, Rodrigo Vivi):

Fixes: c6a4d46ec1d7 ("drm/xe: evict user memory in PM notifier")
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: <stable@vger.kernel.org> # v6.16+
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250904160715.2613-3-thomas.hellstrom@linux.intel.com