drm/i915/color: Make color .get_config() mandatory

Every platforms implements the color .get_config() hook. Just
make it mandatory.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241024165356.17756-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>