shmobile_smp_apmu_prepare_cpus() is used only if CONFIG_SMP=y.

Hence move the #ifdef to cover shmobile_smp_apmu_prepare_cpus() and all
functions only called by it (apmu_init_cpu() and apmu_parse_cfg()).
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>