drm/i915: Implement split/10bit gamma for ivb/hsw

drm/i915: Implement split/10bit gamma for ivb/hsw

Reuse the bdw+ code to get split/10bit gamma for
ivb/hsw. The hardware is nearly identical. The
only slight snag is that on ivb/hsw the precision
palette auto increment mode does not work. So we
must increment the index manually. We'll probably
want to stick to the auto increment mode on bdw+
in the name of efficiency.

Also we want to avoid using the CSC for limited range
RGB output as PIPECONF will take care of that on IVB.

v2: Rebase due to EXT_GC_MAX/EXT2_GC_MAX changes

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190401200231.2333-4-ville.syrjala@linux.intel.com
Reviewed-by: Uma Shankar <uma.shankar@intel.com>