drm/i915: Expose full 1024 LUT entries on ivb+

On ivb+ we can select between the regular 10bit LUT mode with
1024 entries, and the split mode where the LUT is split into
seprate degamma and gamma halves (each with 512 entries). Currently
we expose the split gamma size of 512 as the GAMMA/DEGAMMA_LUT_SIZE.

When using only degamma or gamma (not both) we are wasting half of
the hardware LUT entries. Let's flip that around so that we expose
the full 1024 entries and just throw away half of the user provided
entries when using the split gamma mode.

Cc: Matt Roper <matthew.d.roper@intel.com>
Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401200231.2333-8-ville.syrjala@linux.intel.com


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