drm/amdgpu/display/mst: update mst_mgr relevant variable when long HPD

[Why & How]
Now the vc_start_slot is controlled at drm side. When we
service a long HPD, we still need to run
dm_helpers_dp_mst_write_payload_allocation_table() to update
drm mst_mgr's relevant variable. Otherwise, on the next plug-in,
payload will get assigned with a wrong start slot.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2171


Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Fixes: 4d07b0bc ("drm/display/dp_mst: Move all payload info into the atomic state")
Cc: stable@vger.kernel.org # 6.1
Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Tested-by: Didier Raboud <odyx@debian.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>