ARM: S5P6440: Add IRQ support

This patch adds IRQ support for S5P6440 CPU.

Signed-off-by: Adityapratap Sharma <aditya.ps@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>