drm/xe/pm: Add lockdep annotation for the pm_block completion

drm/xe/pm: Add lockdep annotation for the pm_block completion

Similar to how we annotate dma-fences, add lockep annotation to
the pm_block completion to ensure we don't wait for it while holding
locks that are needed in the pm notifier or in the device
suspend / resume callbacks.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://lore.kernel.org/r/20250918142848.21807-3-thomas.hellstrom@linux.intel.com