drm/amd/display: clear remote dc_sink when stop mst

[Why]
Currently, we don't have code path to release remote dc_sink when unplug
MST hub from the system. After few times hotplug, we hit the limition of
maximum number of remote dc_sink and can't light up new connected monitor
anymore.

[How]
Releasing all remote dc_sink at dm_helpers_dp_mst_stop_top_mgr() was
removed by previous patch. Restore it.
Reviewed-by: NJerry Zuo <Jerry.Zuo@amd.com>
Acked-by: NSolomon Chiu <solomon.chiu@amd.com>
Signed-off-by: NWayne Lin <Wayne.Lin@amd.com>
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -451,6 +451,7 @@ bool dm_helpers_dp_mst_stop_top_mgr(
 		struct dc_link *link)
 {
 	struct amdgpu_dm_connector *aconnector = link->priv;
+	uint8_t i;
 
 	if (!aconnector) {
 		DRM_ERROR("Failed to find connector for link!");
@@ -460,9 +461,26 @@ bool dm_helpers_dp_mst_stop_top_mgr(
 	DRM_INFO("DM_MST: stopping TM on aconnector: %p [id: %d]\n",
 			aconnector, aconnector->base.base.id);
 
-	if (aconnector->mst_mgr.mst_state == true)
+	if (aconnector->mst_mgr.mst_state == true) {
 		drm_dp_mst_topology_mgr_set_mst(&aconnector->mst_mgr, false);
 
+		for (i = 0; i < MAX_SINKS_PER_LINK; i++) {
+			if (link->remote_sinks[i] == NULL)
+				continue;
+
+			if (link->remote_sinks[i]->sink_signal ==
+			    SIGNAL_TYPE_DISPLAY_PORT_MST) {
+				dc_link_remove_remote_sink(link, link->remote_sinks[i]);
+
+				if (aconnector->dc_sink) {
+					dc_sink_release(aconnector->dc_sink);
+					aconnector->dc_sink = NULL;
+					aconnector->dc_link->cur_link_settings.lane_count = 0;
+				}
+			}
+		}
+	}
+
 	return false;
 }