drm/amd/display: Apply fake sink back to MST sequence

[Why]
It fixes the failure to create stream for sink in the scenario
when hotplug SST and MST in sequence, and disconnect MST.

[How]
Add the fake sink back after the majority of MST rework is done.
Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -2959,11 +2959,9 @@ create_stream_for_sink(struct amdgpu_dm_connector *aconnector,
 	drm_connector = &aconnector->base;
 
 	if (!aconnector->dc_sink) {
-		if (!aconnector->mst_port) {
-			sink = create_fake_sink(aconnector);
-			if (!sink)
-				return stream;
-		}
+		sink = create_fake_sink(aconnector);
+		if (!sink)
+			return stream;
 	} else {
 		sink = aconnector->dc_sink;
 	}

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

@@ -173,6 +173,9 @@ static int dm_dp_mst_get_modes(struct drm_connector *connector)
 		aconnector->edid = edid;
 	}
 
+	if (aconnector->dc_sink && aconnector->dc_sink->sink_signal == SIGNAL_TYPE_VIRTUAL)
+		dc_sink_release(aconnector->dc_sink);
+
 	if (!aconnector->dc_sink) {
 		struct dc_sink *dc_sink;
 		struct dc_sink_init_data init_params = {