drm/amd/display: retain/release stream pointer in link enc table

[why]
At every reference to stream pointer, we need to increment/decrement the
kref_count.  Not doing so will result in invalid stream pointer still
alive after hibernate cycle.

[how]
Call stream retain/release whenever the link encoder assignment is set
to true/false since it indicates if we want to reference the stream
pointer or not.
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Sung Joon Kim <sungkim@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -122,6 +122,7 @@ static void remove_link_enc_assignment(
 				stream->link_enc = NULL;
 				state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[i].eng_id = ENGINE_ID_UNKNOWN;
 				state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[i].stream = NULL;
+				dc_stream_release(stream);
 				break;
 			}
 		}
@@ -144,6 +145,7 @@ static void add_link_enc_assignment(
 		 */
 		for (i = 0; i < state->stream_count; i++) {
 			if (stream == state->streams[i]) {
+				dc_stream_retain(stream);
 				state->res_ctx.link_enc_cfg_ctx.link_enc_assignments[i] = (struct link_enc_assignment){
 					.valid = true,
 					.ep_id = (struct display_endpoint_id) {