drm/amd/display: Revert "Directly retrain link from debugfs"

This reverts commit f5b6a20c

.

This patch broke new settings from taking effect. Hotplug is
required for new settings to take effect.

Reviewed-by: Mikita Lipski <mikita.lipski@amd.com>
Acked-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Anson Jacob <Anson.Jacob@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>