shell: device_service: refine level output

Fix the order so that it reflects the actual initialization order,
rather than putting PRE_KERNEL initializations after APPLICATION.

Add SMP in the proper location.

Use the helper function to provide unique identifiers for "devices"
that don't have a device pointer (so don't have a name).

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