drm/amd/display: skip CLEAR_PAYLOAD_ID_TABLE if device mst_en is 0

[Why]
Some dock and mst monitor don't like to receive CLEAR_PAYLOAD_ID_TABLE
when mst_en is set to 0. It doesn't make sense to do so in source
side, either.

[How]
Don't send CLEAR_PAYLOAD_ID_TABLE if mst_en is 0
Reviewed-by: George Shen <George.Shen@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Peichen Huang <PeiChen.Huang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/link/link_dpms.c

@@ -2160,6 +2160,7 @@ static enum dc_status enable_link_dp_mst(
 		struct pipe_ctx *pipe_ctx)
 {
 	struct dc_link *link = pipe_ctx->stream->link;
+	unsigned char mstm_cntl;
 
 	/* sink signal type after MST branch is MST. Multiple MST sinks
 	 * share one link. Link DP PHY is enable or training only once.
@@ -2168,7 +2169,9 @@ static enum dc_status enable_link_dp_mst(
 		return DC_OK;
 
 	/* clear payload table */
-	dm_helpers_dp_mst_clear_payload_allocation_table(link->ctx, link);
+	core_link_read_dpcd(link, DP_MSTM_CTRL, &mstm_cntl, 1);
+	if (mstm_cntl & DP_MST_EN)
+		dm_helpers_dp_mst_clear_payload_allocation_table(link->ctx, link);
 
 	/* to make sure the pending down rep can be processed
 	 * before enabling the link