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

commit 1131cadf upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>