drm/amd/display: Support UHBR10 link rate on eDP

[why]
Supporting UHBR10 link rate on eDP leverages
the existing DP2.0 code but need to add some small
adjustments in code.

[how]
Acknowledge the given DPCD caps for UHBR10
link rate support and allow DP2.0 programming
sequence and link training for eDP.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Sung Joon Kim <Sungjoon.Kim@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>