ARM: EXYNOS4: Remove PMU configuration for S2RAM

PMU(Power Management Unit) configuraion for S2RAM(SLEEP) is removed
and using function which provided by PMU support code to configure
PMU register.

Signed-off-by: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>