drivers/gpio: gpio-nomadik: Add support for irqdomains

Add irq domain support to the gpio-nomadik GPIO driver. This
enables its users to support dynamic IRQ assignment, which is
requried by Device Tree.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>