drm/i915: Make the pipe/output CSC register writes lockless

drm/i915: Make the pipe/output CSC register writes lockless

The pipe/output CSC register writes don't need to be locked
since all the registers are suitably isolated to their own
cachelines. So eliminate the locks to reduce the overhead
during the vblank evade critical section.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220202111616.1579-2-ville.syrjala@linux.intel.com
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>