drm/i915: Implement CTM property support for VLV

VLV has a so called "wide gamut color correction" unit (WGC).
What it is is a 3x3 matrix similar to the later CHV CGM
CSC, with less precisions/range. In fact CHV also has the WGC
but using it there doesn't really make sense when you have the
superior CGM CSC around.

Hook up the necessary stuff to expose the WGC as the CTM
crtc property.

One additional crazy idea that came to mind would be to use
the WGC as an output CSC on CHV for YCbCr output. But it
would be incompatible with the legacy LUT usage. In fact
since the WGC lacks post-offsets we'd probably have to
use the legacy LUT to do that final part of the RGB->YCbCr
conversion. Sounds doable, but perhaps not worth the hassle.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230413164916.4221-6-ville.syrjala@linux.intel.com


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