ARM: EXYNOS: remove exynos4_scu_enable()

The exynos4_scu_enable() is a duplication of scu_enable().  Since
commit '26a527e6 ARM: 7100/1: smp_scu: remove __init annotation from
scu_enable()' makes scu_enable() available for non-init codes, exynos
can directly call scu_enable() and save exynos4_scu_enable() now.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
[kgene.kim@samsung.com: added missing header]
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>