ARM: shmobile: Shared APMU SMP support code without DT

Introduce shared APMU SMP code for mach-shmobile. Both SMP boot up
and CPU Hotplug is supported. This version does not use DT but
if needed this will be added as an incremental feature patch.

The code is designed around CONFIG_NR_CPUS and should in theory support
any number of APMUs, however due to the current DT-less static design
only a single APMU is supported.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>