ARM: EXYNOS: fix non-SMP builds for EXYNOS4

This patch fixes the following build issue, which happens only if
SMP has been disabled:

arch/arm/mach-exynos/built-in.o: In function `exynos4_pm_resume':
arch/arm/mach-exynos/pm.c:387: undefined reference to `scu_enable'

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>