bnx2x: Change BCM848xx configuration according to IEEE

Change BCM848xx behavior to fit IEEE such that setting 10Mb/100Mb will
use force speed, and setting 1Gb/10Gb will use auto-negotiation with the
specific speed advertised

Signed-off-by: Yaniv Rosner <yanivr@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>