drm/i915: Assert {pre,post}_csc_lut were assigned sensibly

Since we now have the extra step from hw.(de)gamma_lut into
{pre,post}_csc_lut let's make sure we didn't forget to assign
them appropriately. Ie. basically making sure intel_color_check()
was called when necessary (and that it did its job suitable well).

Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221024161514.5340-4-ville.syrjala@linux.intel.com