ARM: EXYNOS4: CPUIDLE Support

This patch supports cpuidle framework for EXYNOS4210. Currently,
Only one idle state is possible to use, but more idle states can
be added following by this patch.

Signed-off-by: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>