ARMV7: Exynos4: Add supoort power for Exynos4

This patch adds power.h and SAMSUNG_BASE() macro for using Exynos4 power.

Signed-off-by: HeungJun, Kim <riverful.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>