ARM: EXYNOS: Add generic cpu power control functions for exynos SoCs

Add generic cpu power control functions for exynos based
SoCS for cpu power up/down and to know the cpu status.

Signed-off-by: Leela Krishna Amudala <leela.krishna@linaro.org>
Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>