usb: ulpi: ulpi_init should be executed in subsys_initcall

Phy drivers and the ulpi interface providers depend on the
registration of the ulpi bus.  Ulpi registers the bus in
module_init(). This could cause unnecessary bus users'
probe delays. i.e. unnecessary -EPROBE_DEFER happening on
ulpi_drivers in case they're registered before ulpi bus
itself.
Reported-by: Zhuo Qiuxu <qiuxu.zhuo@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/common/ulpi.c

@@ -242,7 +242,7 @@ static int __init ulpi_init(void)
 {
 	return bus_register(&ulpi_bus);
 }
-module_init(ulpi_init);
+subsys_initcall(ulpi_init);
 
 static void __exit ulpi_exit(void)
 {