drm/amd/display: Release MST resources on switch from MST to SST

[why]
When OS overrides training link training parameters
for MST device to SST mode, MST resources are not
released and leak of the resource may result crash and
incorrect MST discovery during following hot plugs.

[how]
Retaining sink object to be reused by SST link and
releasing MST  resources.

Signed-off-by: Vladimir Stempen <[email protected]>
Reviewed-by: Wenjing Liu <[email protected]>
Acked-by: Stylon Wang <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

Author: vstempen

drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c

@@ -1917,6 +1917,8 @@ static void set_dp_mst_mode(struct dc_link *link, bool mst_enable)
 		link->type = dc_connection_single;
 		link->local_sink = link->remote_sinks[0];
 		link->local_sink->sink_signal = SIGNAL_TYPE_DISPLAY_PORT;
+		dc_sink_retain(link->local_sink);
+		dm_helpers_dp_mst_stop_top_mgr(link->ctx, link);
 	} else if (mst_enable == true &&
 			link->type == dc_connection_single &&
 			link->remote_sinks[0] != NULL) {