drm/xe: Add xe_tlb_inval_idle helper

drm/xe: Add xe_tlb_inval_idle helper

Introduce the xe_tlb_inval_idle helper to detect whether any TLB
invalidations are currently in flight. This is used in context-based TLB
invalidations to determine whether dummy TLB invalidations need to be
sent to maintain proper TLB invalidation fence ordering..

v2:
 - Implement xe_tlb_inval_idle based on pending list

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Tested-by: Stuart Summers <stuart.summers@intel.com>
Link: https://patch.msgid.link/20260116221731.868657-10-matthew.brost@intel.com