ARM: pxa3xx: enable external wakeup pins

The PXA3xx SoCs feature dedicated pins for wakeup functionality. These pins
have no alternate functions, so let's always enable them as wakeup source on
DT enabled boards. The WAKEUP1 pin is only available on PXA320.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>