net: dsa: mv88e6060: setup random mac address

As for mv88e6xxx, setup the switch from within the mv88e6060 driver with
a random MAC address, and remove the .set_addr implementation.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>