bnx2x: Support Queue Per Cos in 5771xx devices

Enable the use of up to three hardware queues for transmission. The queues
are always dequed round robin (i.e. strict priority, PFC and ETS are not
supported). This does allow the allocation of a seperate HW queue for low
volume, high priority traffic which will be serviced more promptly.

Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>