[Why]
It is nice to have link training and link loss status logging in
our trace, and this patch add the all necessary accessors in dc
side.

[How]
1. Define dp_trace struct and create new file link_dp_trace.c and
link_dp_trace.h;
2. Add dp link training status update in dc_link_dp.c;
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>