net: usb: ax88179_178a: allow optionally getting mac address from device tree

Adopt and integrate the feature to pass the MAC address via device tree
from asix_device.c (03fc5d4f) also to other ax88179 based asix chips.
E.g. the bootloader fills in local-mac-address and the driver will then
pick up and use this MAC address.

Signed-off-by: Peter Fink <pfink@christ-es.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>