drm/i915: Add max_bpc property for DP MST

Allow the user to limit the output bpc with DP MST.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326142556.21176-4-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_dp_mst.c

@@ -530,6 +530,7 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 
 	intel_attach_force_audio_property(connector);
 	intel_attach_broadcast_rgb_property(connector);
+	drm_connector_attach_max_bpc_property(connector, 6, 12);
 
 	return connector;