ARM: shmobile: armadillo800eva: USB Func enables external IRQ mode

We can control renesas_usbhs driver as 2 way which are
autonomy mode and external IRQ trigger mode.

Autonomy mode is very easy settings for platform,
but it required USB power domain always ON,
since its connection/disconnection IRQ come from it.

If platform uses external IRQ trigger mode,
USB power domain can be OFF, since its
connection/disconnection IRQ come from external IRQ.

This patch enable external IRQ mode.
Now it is possible to add USB support on A4SP domain.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>