ARM: EXYNOS4: Add functions for gic interrupt handling

This patch adds two functions for gic interrupt handling.
1. Add interrupt handling of 4 cores.
2. Dynamically set gic bank offset according to the type of soc.
   Gic bank offset of EXYNOS4412 is 0x4000 while the offset of
   EXYNOS4210 and EXYNOS4212 is 0x8000.

This patch is necessary because EXYNOS4 socs cannot support
GIC register banking as described in commit aab74d3e75364.

Signed-off-by: Changhwan Youn <chaos.youn@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>