drm/i915/tc: Call TypeC port flush_work/cleanup without modeset locks held

Call the TypeC port flush_work and cleanup handlers without the modeset
locks held. These don't require the locks, as the work takes - as it
should be able to at any point in time - any locks it needs and by the
time cleanup is called and after cleanup returns the encoder is not in
use.

This is required by the next patch canceling a TypeC port work
synchronously during encoder suspend and shutdown, where the work can
take modeset locks as well, hence the canceling must be done without
holding the locks.

I also considered moving the modeset locking down to each encoder
suspend()/shutdown() hook instead, however locking the full modeset
state for each encoder separately would be odd, and the bigger change -
affecting all encoders - is beyond the scope of this patchset.

v2:
- Add a TODO: comment to remove modeset locks if no encoder depends
  on this. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230512195513.2699-1-imre.deak@intel.com