ARM: EXYNOS4: Add support PM for EXYNOS4212

This patch moves regarding clock stuff of PM into clock
file to support PM on EXYNOS4210 and EXYNOS4212 with one
single kernel image. Because some clock registers are
different on each SoCs.

Signed-off-by: Jonghwan Choi <jhbird.choi@samsung.com>
[kgene.kim@samsung.com: use CONFIG_PM_SLEEP instead of CONFIG_PM]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>