drm/i915: s/gamma/post_csc_lut/

Rename a the LUT state check foo_gamma_precision() functions
to foo_post_csc_lut_precision() to make it more clear what
they really do.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221114153732.11773-8-ville.syrjala@linux.intel.com


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