drm/amd/display: Directly retrain link from debugfs

[why/how]
Skip logic that sets preffered link settings
and just retrain with new link_settings from Debugfs

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>