board/aarch64: use %m modifier in default xPi hostnames

The xPi's usually don't have a VPD so the chassis mac-address probed at
boot is usually null in /run/system.json.  This commit adds a fallbkack
mechanism to populate this field so it can be used for unique hostnames
even on these boards.

Ths ietf-hardware.yang model does not have a notion of physical address,
so we augment one tht is generic enought to be used for other hardware
components than Ethernet, similar to what ietf-interfaces.yang use.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/statd/python/cli_pretty/cli_pretty.py

@@ -1703,6 +1703,8 @@ def show_hardware(json):
             print(f"Manufacturer        : {board['mfg-name']}")
         if board.get("serial-num"):
             print(f"Serial Number       : {board['serial-num']}")
+        if board.get("infix-hardware:phys-address"):
+            print(f"Base MAC Address    : {board['infix-hardware:phys-address']}")
         if board.get("hardware-rev"):
             print(f"Hardware Revision   : {board['hardware-rev']}")