drm/i915: Split ivb_load_lut_ext_max() into two parts

drm/i915: Split ivb_load_lut_ext_max() into two parts

Split the EXT2_MAX register programming into its own function.
More in line with the whole "cobble together stuff from small
pieces" approach used in this code.

The EXT(2)_MAX registers are also not really part of the
multi-segment section of the LUT, so hoist the calls to a
higher level, just like we do in other gamma modes as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221026113906.10551-6-ville.syrjala@linux.intel.com
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>