drm/amd/display: Move link_trace for edp to dp_trace

[Why & How]
The dp_trace structure is self contained component designed for
all dp trace, and the edp link trace should be a part of it;

Suggested-by: Wenjing Liu <wenjing.liu@amd.com>

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>