drm/amd/display: Add DP 2.0 MST DM Support

[Why]
Add DP2 MST and debugfs support

[How]
Update the slot info based on the link encoding format

Reviewed-by: "Lin, Wayne" <Wayne.Lin@amd.com>
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211025223825.301703-5-lyude@redhat.com