pinctrl: exynos5440: add gpio interrupt support

Exynos5440 supports gpio interrupts on gpios 16 to 23. The eight interrupt lines
originating from the pin-controller are connected to the gic. Add irq-chip support
for these interrupts.

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>