libpayload: Add USB support for non-PCI controllers

Restructure USB stack to not depend on PCI, and
make PCI stub available on x86, but provide fixed
BARs for ARM (Exynos 5)

Change-Id: Iee7c8b134c22b661a9a515e24943470c9dbadd1f
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/49970
Reviewed-on: http://review.coreboot.org/4175
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

payloads/libpayload/drivers/usb/usbmsc.c

@@ -27,6 +27,7 @@
  * SUCH DAMAGE.
  */
 
+//#define USB_DEBUG
 #include <endian.h>
 #include <usb/usb.h>
 #include <usb/usbmsc.h>