bnx2x: PFC support for 578xx

Add supoprt for 3 COSes for 578xx devices.
Fix HW configuration for PFC feature according to new HSI in link layer.

Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Vladislav Zolotarov <vladz@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>