In many parts of the computing world having a unique MAC address
sitting in some on-NIC storage is considered the normal case.
Remove the warning to not scare the user unnecessarily.
This applies to Highbank/Midway and ARM's Juno, for instance.
Besides that this fixes the formatting on Midway, for instance,
which currently looks like:
...
Net:   xgmac0
Warning: xgmac0 using MAC address from net device
, xgmac1
Warning: xgmac1 using MAC address from net device
...

Signed-off-by: Andre Przywara <andre.przywara@arm.com>