igb: Add Energy Efficient Ethernet (EEE) for i350 devices.

This patch adds the EEE feature for i350 devices, enabled by default.

Signed-off-by: Carolyn Wyborny <carolyn.wyborny@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>