doc: services: pm: update pm device init/deinit/states

- Specify "Device" Power Management Support in sections covering
  CONFIG_PM_DEVICE=y or n
- Extend the enum pm_device_state docstrings to define and detail
  expectations of devices in each enum pm_device_state state.
- Extend pm device driver code example with more concise comments
  and include pm_device_driver_init, pm_device_driver_deinit, and
  DEVICE_DT_INST_DEINIT_DEFINE() (device deinit feature)
- Describe the device driver PM states used if PM_DEVICE is not
  enabled.
- Note which states a device driver is initialized from and can
  be deinitialized in and why.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>