usbdebug: Move initialisation of the optional hub

Add new file for device-specific initialisation transactions.

Change-Id: I339df400a41675f178c7af613f03b2b44c826189
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7208
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins)

src/drivers/usb/ehci.h

@@ -197,4 +197,7 @@ struct ehci_dbg_port {
 	u32	address;
 #define DBGP_EPADDR(dev, ep)	(((dev)<<8)|(ep))
 } __attribute__ ((packed));
+
+#define USB_DEBUG_DEVNUM 127
+
 #endif