usbdebug: Move under drivers/usb

Also relocate and split header files, there is some interest
for EHCI debug support without PCI.

Change-Id: Ibe91730eb72dfe0634fb38bdd184043495e2fb08
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5129
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/southbridge/intel/i82801dx/usb2.c

@@ -24,7 +24,7 @@
 #include <device/pci.h>
 #include <device/pci_ids.h>
 #include <device/pci_ops.h>
-#include <usbdebug.h>
+#include <device/pci_ehci.h>
 #include "i82801dx.h"
 
 static void usb2_init(struct device *dev)