drm/amd/display: Add tags for indicating mst progress status

[Why & How]
In order to leverage igt tool to maintain mst feature, expose new
debugfs entry "mst_progress_status".

In our dm flow, record down the result of each phase of mst and user
can examine the mst result by checking whether each phase get completed
successfully.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>