tg3: Poll cpmu link state on APE + ASF enabled devices

On ASF enabled devices where the mgmt firmware runs on the application
processing engine, there is a race between the tg3 driver processing a
link change event and the ASF firmware clearing the link changed bit in
the EMAC status register. This leads to link notifications to the driver
sometimes getting lost.

Poll the CPMU link state as a backup for the normal interrupt path
update if ASF is enabled.

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