bcm87xx: disable autonegotiation by default

The bcm87xx phys don't support autonegotiation, so don't use it by
default, as otherwise phy_state_machine() will try to enable it (using
c22 requests, which also don't make any sense for the bcm78xx).

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>