PM / Runtime: Add subsystem data field to struct dev_pm_info

Some subsystems need to attach PM-related data to struct device and
they need to use devres for this purpose.  For their convenience
and to make code more straightforward, add a new field called
subsys_data to struct dev_pm_info and let subsystems use it for
attaching PM-related information to devices.

Convert the ARM shmobile platform to using the new field.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>