tests: pm: device_runtime: add test for the API

Add a test for the device runtime API that makes sure most common usage
scenarios behave as expected:

- get + put
- get + asynchronous put until suspended
- get + asynchronous put + get (while suspend still ongoing)

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