drm/amd/display : Log DP link training failure reason

[Why]
Existing logs doesn't print DP LT failure reason

[How]
Update the existing log with DP LT failure reason

Signed-off-by: Chandan Vurdigere Nataraj <chandan.vurdigerenataraj@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>