pinctrl: at91-pio4: add PM stuff

Allow GPIOs to be configured as wakeup sources. When going to suspend,
disable all GPIO irqs excepting the one configured as wakeup sources.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>