ixgbe: add support for 82599 Combined Backplane

This patch will add support for the 82599 Dual port Backplane
device (0x10f8).  This device has the ability to link in serial (KR) and
parallel (KX4/KX) modes, depending on what the switch capabilities are in
the blade chassis.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Acked-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>