ixgbe: add support for X540-AT1

This patch adds device support for Ethernet Controller X540-AT1.

Signed-off-by: Josh Hay <joshua.a.hay@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>