bnx2x: Take chip version from MFW

In latest boards, the CHIP_METAL register contains an incorrect
revision value, so the correct one needs to be obtained in a
different manner.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
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>