drm/amd/display: force TBT4 dock dsc on

[why]
TBT4 dock have bandwidth limitation, need dsc always on to support all
modes.

[how]
force dsc always on when detect TBT4 dock.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Fudongwang <Fudong.Wang@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>