pm: device: runtime: remove pm_device_get_async

As of today there is no clear usage of asynchronous gets, since in
general, a resume operation should be synchronous (we are about to use
the device immediately after resuming it). Removing this API simplifies
the runtime implementation in a significant way (refer to future
commits).

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
6 files changed