ARM: mach-shmobile: Runtime PM late init callback

Add a mach-shmobile specific callback for SoC-specific code
to hook into. By having the late_initcall() in a common place
we can have multi-SoC/board support in the same kernel binary.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>