e1000e: Add support for EEE in Sx states

On I217 and newer hardware, EEE is enabled in the PHY by the software
when link is up and disabled by the hardware when link is lost.

To enable EEE in Sx (When both ends of the link support, and are enabled
for, EEE and 100Mbps), we need to disable LPLU and configure the PHY to
automatically enable EEE when link is up, since there will be no software
to complete the task.

To configure this in the PHY, the Auto Enable LPI bit in the Low Power
Idle GPIO Control register must be set.  For normal operation in S0, this
bit must be cleared.

Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>