e1000e: enable support for EEE on 82579

This patch enables IEEE802.3az (a.k.a. Energy Efficient Ethernet) on the
new 82579 LOMs.  An optional module parameter is provided to disable the
feature if desired.

Signed-off-by: Bruce Allan <bruce.w.allan@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>