ARM: mach-shmobile: Suspend-to-RAM support

This patch adds a simple Suspend-to-RAM implementation
for SH-Mobile ARM. The struct shmobile_suspend_ops are
kept global to allow cpu-specific code to override
the callbacks if needed.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>