Revert "drm/amd/display: Disable virtual links"

This reverts commit b22c3362.

[WHY & HOW]
The writeback series cause a regression in thunderbolt display.
Signed-off-by: Alex Hung <alex.hung@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1676,7 +1676,7 @@ static int amdgpu_dm_init(struct amdgpu_device *adev)
 
 	/* Enable DWB for tested platforms only */
 	if (adev->ip_versions[DCE_HWIP][0] >= IP_VERSION(3, 0, 0))
-		init_data.num_virtual_links = 0;
+		init_data.num_virtual_links = 1;
 
 	INIT_LIST_HEAD(&adev->dm.da_list);