usbdebug: Use CAR migration

If we already initialized EHCI controller and USB device in romstage,
locate active configuration from salvaged CAR_GLOBAL and avoid doing
the hardware initialisation again.

Change-Id: I7cb3a359488b25abc9de49c96c0197f6563a4a2c
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3476
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/include/cbmem.h

@@ -70,6 +70,7 @@
 #define CBMEM_ID_ROOT		0xff4007ff
 #define CBMEM_ID_VBOOT_HANDOFF	0x780074f0
 #define CBMEM_ID_CAR_GLOBALS	0xcac4e6a3
+#define CBMEM_ID_EHCI_DEBUG	0xe4c1deb9
 #define CBMEM_ID_NONE		0x00000000
 #define CBMEM_ID_AGESA_RUNTIME	0x41474553