drm/xe: Wait on in-syncs when swicthing to dma-fence mode

drm/xe: Wait on in-syncs when swicthing to dma-fence mode

If a dma-fence submission has in-fences and pagefault queues are running
work, there is little incentive to kick the pagefault queues off the
hardware until the dma-fence submission is ready to run. Therefore, wait
on the in-fences of the dma-fence submission before removing the
pagefault queues from the hardware.

v2:
 - Fix kernel doc (CI)
 - Don't wait under lock (Thomas)
 - Make wait interruptable

Suggested-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20251212182847.1683222-6-matthew.brost@intel.com