drm/amd/display: add workaround for 4k video underflow

drm/amd/display: add workaround for 4k video underflow

[Why]
On DCN1, there is an issue where on high BW config on single channel
systems, underflow will be observed if DCC is disabled. This issue
can be observed on several use cases. For this particular case,
it is observed when playing 4k video on 4k desktop with video downscaled
to a certain size.

[How]
Block MPO for this particular case, this will prevent extra BW consumed
from downscaling, working around the underflow.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>