shell: device_service: print DT metadata

Example output on qemu_cortex_m3:

  devices:
  - uart@4000e000 (READY)
    DT node labels: uart2
  - uart@4000d000 (READY)
    DT node labels: uart1
  - uart@4000c000 (READY)
    DT node labels: uart0
  - gpio@40026000 (READY)
    DT node labels: gpio6
  - gpio@40025000 (READY)
    DT node labels: gpio5
  - gpio@40024000 (READY)
    DT node labels: gpio4
  - gpio@40007000 (READY)
    DT node labels: gpio3
  - gpio@40006000 (READY)
    DT node labels: gpio2
  - gpio@40005000 (READY)
    DT node labels: gpio1
  - gpio@40004000 (READY)
    DT node labels: gpio0

Signed-off-by: Martí Bolívar <mbolivar@amperecomputing.com>