drm/xe: Save off position in ring in which a job was programmed

drm/xe: Save off position in ring in which a job was programmed

VF post-migration recovery needs to modify the ring with updated GGTT
addresses for pending jobs. Save off position in ring in which a job was
programmed to facilitate.

v4:
 - s/VF resume/VF post-migration recovery (Tomasz)

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Tomasz Lis <tomasz.lis@intel.com>
Link: https://lore.kernel.org/r/20251008214532.3442967-3-matthew.brost@intel.com