drm/amd/display: avoid link loss short pulse stuck the system

[Why]
MST monitor sends link loss short pulse continuous but sink is
occupy by HDMI input to lead link training fail.

[How]
disable link once retraining fail.

Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Yu-ting Shen <yu-tshen@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>