ARM: EXYNOS4: Add support for gpio interrupts

This patch adds support for gpio interrupts on Samsung EXYNOS4 platform.
Common s5p-gpioint.c code is used for handling gpio interrupts. Each gpio
line that needs gpio interrupt support must be later registered with
s5p_register_gpio_interrupt() function.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>