ARM: EXYNOS: Remove scu_enable from cpuidle

Cortex A9 based exynos4 has a memory mapped SCU while the Cortex
A15 based exynos5 does not. Hence, remove the call to scu_enable
for exynos5.

Signed-off-by: Abhilash Kesavan <a.kesavan@samsung.com>
Signed-off-by: Inderpal Singh <inderpal.singh@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>