OMAP: PM: omap_device: add API to disable idle on suspend

By default, omap_devices will be automatically idled on suspend
(and re-enabled on resume.)  Using this new API, device init code
can disable this feature if desired.

NOTE: any driver/device that has been runtime PM converted should
      not be using this API.

Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>