drm/i915/dsb: Use non-locked register access

Avoid the locking overhead for DSB registers. We don't need the locks
and intel_dsb_commit() in particular needs to be called from the
vblank evade critical section and thus needs to be fast.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606191504.18099-3-ville.syrjala@linux.intel.com


Reviewed-by: Uma Shankar <uma.shankar@intel.com>