igc: Add PHY power management control

PHY power management control should provide a reliable and accurate
indication of PHY reset completion and decrease the delay time
after a PHY reset

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>