drm/i915: Intruduce display.wq.cleanup

drm/i915: Intruduce display.wq.cleanup

Introduce a dedicated workqueue for the commit cleanup work.
In the future we'll need this to guarantee all the cleanup
works have finished at a specific point during suspend.

Cc: Brian Geffon <bgeffon@google.com>
Cc: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241127061117.25622-3-ville.syrjala@linux.intel.com
Reviewed-by: Vidya Srinivas <vidya.srinivas@intel.com>
Tested-by: Vidya Srinivas <vidya.srinivas@intel.com>