of: overlay_mgr: Allow using devices at root in overlay

Move of_overlay_mgr_init to run after of_platform_default_populate_init.
If of_overlay_mgr_init runs first, then the overlays will be processed
while the bus is being populated. This prevents the notifier from
working and will prevent adding devices to the root (or any other parent
bus of the overlay_mgr device).

Change-Id: I4622edfc34f16ef4e549d30d518af884c669b5bd
Signed-off-by: Arve Hjønnevåg <arve@android.com>

drivers/of/overlay_mgr.c

@@ -149,4 +149,4 @@ static int __init of_overlay_mgr_init(void)
 	return platform_driver_register(&of_overlay_mgr_driver);
 }
 
-postcore_initcall(of_overlay_mgr_init);
+subsys_initcall(of_overlay_mgr_init);