drm/i915: Fix CHV CGM CSC coefficient sign handling

The CHV CGM CSC coefficients are in s4.12 two's complement
format. Fix the CTM->CGM conversion to handle that correctly
instead of pretending that the hw coefficients are also
in some sign-magnitude format.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230413164916.4221-4-ville.syrjala@linux.intel.com


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