[TG3]: Improve 5704S autoneg.

Improve 5704S autoneg logic by using a serdes_counter field to keep
track of the transient states.  This eliminates a 200 msec busy
loop in the code.  Autoneg will take its course without the driver
busy waiting for it to finish.

Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>