drm/i915: Get rid of glk_load_degamma_lut_linear()

Since we now have a place (pre_csc_lut) to stuff a purely
internal LUT we can replace glk_load_degamma_lut_linear()
with such a thing and just rely on the normal
glk_load_degamma_lut() to load it as well.

drm_mode_config_cleanup() will clean this up for us.

v2: Pass on the error pointer
    Drop a hint about this into the state dump

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/20221024161514.5340-5-ville.syrjala@linux.intel.com