e1000e: Additional PHY power saving in S0ix

After transferring the MAC-PHY interface to the SMBus set the PHY
to S0ix low power idle mode.
Suggested-by: Dima Ruinskiy <dima.ruinskiy@intel.com>
Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/e1000e/netdev.c

@@ -6378,10 +6378,16 @@ static void e1000e_s0ix_entry_flow(struct e1000_adapter *adapter)
 		ew32(CTRL_EXT, mac_data);
 
 		/* DFT control: PHY bit: page769_20[0] = 1
+		 * page769_20[7] - PHY PLL stop
+		 * page769_20[8] - PHY go to the electrical idle
+		 * page769_20[9] - PHY serdes disable
 		 * Gate PPW via EXTCNF_CTRL - set 0x0F00[7] = 1
 		 */
 		e1e_rphy(hw, I82579_DFT_CTRL, &phy_data);
 		phy_data |= BIT(0);
+		phy_data |= BIT(7);
+		phy_data |= BIT(8);
+		phy_data |= BIT(9);
 		e1e_wphy(hw, I82579_DFT_CTRL, phy_data);
 
 		mac_data = er32(EXTCNF_CTRL);