drm/i915/display: remove explicit CNL handling from intel_color.c

The only real platform with DISPLAY_VER == 10 is GLK, so we don't need
any checks and supporting code for CNL. For DISPLAY_VER >= 11,
ilk_load_csc_matrix() is not used, so make it handle GLK only.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728215946.1573015-4-lucas.demarchi@intel.com