aries | p1: arm: s5pv210: fix gcc warning

fix:

/arch/arm/mach-s5pv210/include/mach/system.h:18:13: \
warning: 'arch_idle' defined but not used [-Wunused-function]

Signed-off-by: Humberto Borba <humberos@gmail.com>
Change-Id: I3f8efbc076ddd6c0e4fb6ab118b3de29b59c1905