drm/amd/display: Reset PHY in link re-training

[Why]
Link training failed randomly when plugging USB-C display in/out.

[How]
If link training failed, reset PHY in link re-training.

Signed-off-by: Paul Hsieh <paul.hsieh@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>