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

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

[Why]
configure/call DC interface for DP2 mst support. This is needed to make DP2
mst work.

[How]
- add encoding type, logging, mst update/reduce payload functions

Use the link encoding to determine the DP type (1.4 or 2.0) and add a
flag to dc_stream_update to determine whether to increase/reduce
payloads.

v2:
* add DP_UNKNOWN_ENCODING handling

Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Reviewed-by: "Lin, Wayne" <Wayne.Lin@amd.com>
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211025223825.301703-4-lyude@redhat.com