gpio: dwapb: Add wakeup source support

This patch supports irq_set_wake for dwapb gpio. It allows GPIOs
to be configured as wakeup sources and wake the system from suspend.

Signed-off-by: Hoan Tran <hotran@apm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>