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>