ARM: EXYNOS: use generic exynos cpu power control functions

Use generic exynos cpu power control functions to power up/down
and to know the status of the cpu in platsmp and hotplug code.

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>