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

- Extend the pm device documentation defining and detailing
  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 <[email protected]>

Author: bjarki-andreasen