dm: usb: Add a uclass for USB controllers

Add a uclass that can represent a USB controller. For now we do not create
devices for things attached to the controller. This will be added later.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/drivers/usb/musb-new/musb_uboot.c b/drivers/usb/musb-new/musb_uboot.c
index 053d945..7d90ebc 100644
--- a/drivers/usb/musb-new/musb_uboot.c
+++ b/drivers/usb/musb-new/musb_uboot.c
@@ -180,7 +180,7 @@
 	return NULL; /* URB still pending */
 }
 
-void usb_reset_root_port(void)
+int usb_reset_root_port(void)
 {
 	void *mbase = host->mregs;
 	u8 power;
@@ -208,6 +208,8 @@
 			(musb_readb(mbase, MUSB_DEVCTL) & MUSB_DEVCTL_FSDEV) ?
 			USB_SPEED_FULL : USB_SPEED_LOW;
 	mdelay((host_speed == USB_SPEED_LOW) ? 200 : 50);
+
+	return 0;
 }
 
 int usb_lowlevel_init(int index, enum usb_init_type init, void **controller)