bnx2x: Change MDIO clock settings

When drivers works on top of an old bootcode, it is theoretically subjected to
MDC/MDIO failures since the MDIO clock is set in the beginning of each sequence,
rather than per CL45 command. On rare cases an old bootcodes may change that in
the middle, so to address that, the MDIO clock is set for each CL45 access.
In addition, setting the MDIO clock is now done per EMAC base, and
not per port number, since a specific port can potentially use both EMACs for
different PHY accesses.

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>