ARM: EXYNOS4: Use samsung_rev() to distinguish silicon revision

This patch uses samsung_rev() to support variable silicon revision of
EXYNOS4210 so that can support for EXYNOS4210 REV0, REV1.0 and REV1.1.

Note: Need to change timer setting on REV0.

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