ARM: S3C24XX: move irq driver to drivers/irqchip

This move is necessary to make use of the irqchip infrastructure
for the following devicetree support for s3c24xx architectures.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>