drm/amd/display: Fix allocate_mst_payload assert on resume

[ Upstream commit f4346fb3 ]

[Why]
On resume we do link detection for all non-MST connectors.
MST is handled separately. However the condition for telling
if connector is on mst branch is not enough for mst hub case.
Link detection for mst branch link leads to mst topology reset.
That causes assert in dc_link_allocate_mst_payload()

[How]
Use link type as indicator for mst link.

Reviewed-by: Wayne Lin <Wayne.Lin@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>