drm/i915: Force RGB output for DVI sink

YCbCr output requires infoframes and whatnot, so don't allow
it when dealing with a DVI sink (or a HDMI sink we wish to
treat as DVI).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221107194604.15227-3-ville.syrjala@linux.intel.com


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