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

This reverts commit f5b6a20.

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>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c

@@ -247,6 +247,7 @@ static ssize_t dp_link_settings_write(struct file *f, const char __user *buf,
 {
 	struct amdgpu_dm_connector *connector = file_inode(f)->i_private;
 	struct dc_link *link = connector->dc_link;
+	struct dc *dc = (struct dc *)link->dc;
 	struct dc_link_settings prefer_link_settings;
 	char *wr_buf = NULL;
 	const uint32_t wr_buf_size = 40;
@@ -313,7 +314,7 @@ static ssize_t dp_link_settings_write(struct file *f, const char __user *buf,
 	prefer_link_settings.lane_count = param[0];
 	prefer_link_settings.link_rate = param[1];
 
-	dp_retrain_link_dp_test(link, &prefer_link_settings, false);
+	dc_link_set_preferred_training_settings(dc, &prefer_link_settings, NULL, link, true);
 
 	kfree(wr_buf);
 	return size;