ARM: shmobile: apmu: silence build warnings

With shmobile_defconfig but SMP=n && SUSPEND=n, I get:

arch/arm/mach-shmobile/platsmp-apmu.c:49:12: warning: 'apmu_power_off' defined but not used [-Wunused-function]
arch/arm/mach-shmobile/platsmp-apmu.c:70:12: warning: 'apmu_wrap' defined but not used [-Wunused-function]

Annotate those functions like the functions around it.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>