For USB gadget on port A (device mode):
- pin PA31 is configured as an input GPIO which triggers an interrupt when
  vbus is detected on USB port A.
- pin PB9 is configured as an output GPIO and set to low level so the
  board doesn't supply vbus to USB port A.

For USB host:
- pin PB10 is configured as an output GPIO and is active at high level.
  The ohci driver will activate this pin so the board supplies vbus to USB
  port B.
- pin PB9 should be configured as an output GPIO and active at high level
  to use to USB port A in host mode (conflicts with USB gadget).
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>