drm/xe: Issue GGTT invalidation under lock in ggtt_node_remove

drm/xe: Issue GGTT invalidation under lock in ggtt_node_remove

Async work (e.g., GuC queue teardowns) can call ggtt_node_remove, so the
operation must be performed under the GGTT lock to ensure the GGTT
online check remains stable. GGTT insertion and removal are heavyweight
operations (e.g., queue create/destroy), so the additional serialization
cost is negligible compared to ensuring correctness.

Fixes: 4f3a998a173b ("drm/xe: Open-code GGTT MMIO access protection")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Link: https://patch.msgid.link/20260326011207.62373-1-matthew.brost@intel.com