net: ftgmac100: support getting MAC address from NVMEM

Make use of of_get_ethdev_address() to support reading MAC address not
only from the usual DT nodes but also from an NVMEM provider (e.g. using
a dedicated area in an FRU EEPROM).

Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Link: https://lore.kernel.org/r/20230713095743.30517-1-fercerpav@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>