igc: Remove the polarity field from a PHY information structure

Polarity and cable length fields is not applicable for the i225 device.
This patch comes to clean up PHY information structure.

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>