drm/amd/display: Add DP2 Metrics

Why:
Log DP2 data to be used for debugging purposes

How:
Check the reported link rate of the DP connection and
translate it to the DP version.

Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Austin Zheng <austin.zheng@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>