ARM: EXYNOS4: Add support clock for EXYNOS4212

This patch splits EXYNOS4 clock code to EXYNOS4 common,
EXYNOS4210 and EXYNOS4212 for supporting new EXYNOS4212
SoC with one kernel image. Of course, this patch adds
some clock codes for EXYNOS4212 SoC.

Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>