atphy: Explicitly clear 1000baseT control register for 10/100 only F1 PHY

atphy: Explicitly clear 1000baseT control register for 10/100 only F1 PHY

Obtained-from: FreeBSD 221817

  "Explicitly clear 1000baseT control register for F1 PHY used in
   AR8132 FastEthernet controller.  The PHY has no ability to
   establish a gigabit link. Previously only link parters which
   support down-shifting was able to establish link.
   This change should fix a long standing link establishment issue
   of AR8132."