drm/i915: utilize subconnector property for DP

Since DP-specific information is stored in driver's structures, every
driver needs to implement subconnector property by itself.

v2: updates to match previous commit changes

v3: rebase

v4: renamed a function call

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: Jeevan B <jeevan.b@intel.com>
Signed-off-by: Oleg Vasilev <oleg.vasilev@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com> #and acked for merging
Tested-by: Oleg Vasilev <oleg.vasilev@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1587732655-17544-2-git-send-email-jeevan.b@intel.com

drivers/gpu/drm/i915/display/intel_dp.c

@@ -6256,6 +6256,11 @@ intel_dp_detect(struct drm_connector *connector,
 	 */
 	intel_display_power_flush_work(dev_priv);
 
+	if (!intel_dp_is_edp(intel_dp))
+		drm_dp_set_subconnector_property(connector,
+						 status,
+						 intel_dp->dpcd,
+						 intel_dp->downstream_ports);
 	return status;
 }
 
@@ -7350,6 +7355,9 @@ intel_dp_add_properties(struct intel_dp *intel_dp, struct drm_connector *connect
 	struct drm_i915_private *dev_priv = to_i915(connector->dev);
 	enum port port = dp_to_dig_port(intel_dp)->base.port;
 
+	if (!intel_dp_is_edp(intel_dp))
+		drm_connector_attach_dp_subconnector_property(connector);
+
 	if (!IS_G4X(dev_priv) && port != PORT_A)
 		intel_attach_force_audio_property(connector);