drm/i915: Declare .(de)gamma_lut_tests for icl+

drm/i915: Declare .(de)gamma_lut_tests for icl+

All interpolated gamma modes including the icl+ multi segment
mode require non-decreasing entries for the interpolation to
work correctly. For some reason we're forgetting to declare
that for icl+. Let us do so.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/3916
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014181856.17581-1-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>