shell: device_service: add dependency information

Refactor the output of device list to use standard API to retrieve the
list of devices, and to always display a status rather than hiding
disabled/failed devices.

Add API to associate a distinct identifier with any "device" that does
not have a name.

Where a device has requires dependencies display the devices on which
it depends.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>