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/nvidia/ck804/enable_usbdebug.c

@@ -26,7 +26,7 @@
 
 #include <stdint.h>
 #include <arch/io.h>
-#include <usbdebug.h>
+#include <device/pci_ehci.h>
 #include <device/pci_def.h>
 #include "ck804.h"