This patch adds header <linux/sched.h> into the below files for build with
CONFIG_PREEMPT_NONE.

arch/arm/mach-s5p64x0/cpu.c
Signed-off-by: NSeung-Chull Suh <sc.suh@samsung.com>
[kgene.kim@samsung.com: edited title and message]
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>