ARM: EXYNOS: Add support AFTR mode on EXYNOS4210

This patch adds support AFTR(ARM OFF TOP RUNNING) mode in
cpuidle driver. L2 cache keeps their data in this mode.
This patch ports the code to the latest interfaces to
save/restore CPU state inclusive of CPU PM notifiers, l2
resume and cpu_suspend/resume.

Signed-off-by: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@linaro.org>
[kgene.kim@samsung.com: fixed for non-smp as per Tushar's pointing out]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>