igb: Program MDICNFG register prior to PHY init

This patch addresses an issue seen on 82580 in which the MDICNFG
register will be reset during a single function reset and as a
result we will be unable to communicate with the PHY.  To correct
the issue, added a call to reset_mdicnfg just prior to the first
access of the MDICNFG register in sgnii_uses_mdio.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>