davinci_emac: use eth_hw_addr_random() instead of random_ether_addr()

Use eth_hw_addr_random() instead of calling random_ether_addr()
to set addr_assign_type correctly to NET_ADDR_RANDOM.

Reset the state to NET_ADDR_PERM as soon as the MAC get
changed via .ndo_set_mac_address.

Remove one memcpy from emac_dev_setmac_addr() since this is a
duplicate: it's already done some lines above.

v2: use bitops, adapt to eth_hw_addr_random, remove a memcpy

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: David S. Miller <davem@davemloft.net>