ARM: SAMSUNG: Add common samsung_gpiolib_to_irq function

This patch adds a common callback for gpio_to_irq() for external and
gpio interrupts for Samsung SoCs.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Ben Dooks <ben-linux@fluff.org>
[kgene.kim@samsung.com: moved samsung_gpiolib_to_irq() for s3c24xx build]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>