drm/i915/dp: Support DP ports YUV 4:2:0 output to GEN11

Bspec describes that GEN10 only supports capability of YUV 4:2:0 output to
HDMI port and GEN11 supports capability of YUV 4:2:0 output to both DP and
HDMI ports.

v2: Minor style fix.
Signed-off-by: NGwan-gyeong Mun <gwan-gyeong.mun@intel.com>
Reviewed-by: NMaarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190521121721.32010-7-gwan-gyeong.mun@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -7395,6 +7395,9 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 		connector->interlace_allowed = true;
 	connector->doublescan_allowed = 0;
 
+	if (INTEL_GEN(dev_priv) >= 11)
+		connector->ycbcr_420_allowed = true;
+
 	intel_encoder->hpd_pin = intel_hpd_pin_default(dev_priv, port);
 
 	intel_dp_aux_init(intel_dp);