drm/i915/dsb: Don't use DSB to load the LUTs during full modeset

Using the DSB for LUT loading during full modesets would require
some actual though. Let's just use mmio for the time being.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230606191504.18099-12-ville.syrjala@linux.intel.com


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