igb: Implement support to power sfp cage and turn on I2C

Based on original patch from Aurélien Guillaume <footplus@gmail.com>
This patch adds support to turn on I2C, with sfp cage powered.

CC: Aurélien Guillaume <footplus@gmail.com>
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/e1000_82575.c

@@ -1420,9 +1420,10 @@ static s32 igb_setup_serdes_link_82575(struct e1000_hw *hw)
 	 */
 	wr32(E1000_SCTL, E1000_SCTL_DISABLE_SERDES_LOOPBACK);
 
-	/* power on the sfp cage if present */
+	/* power on the sfp cage if present and turn on I2C */
 	ctrl_ext = rd32(E1000_CTRL_EXT);
 	ctrl_ext &= ~E1000_CTRL_EXT_SDP3_DATA;
+	ctrl_ext |= E1000_CTRL_I2C_ENA;
 	wr32(E1000_CTRL_EXT, ctrl_ext);
 
 	ctrl_reg = rd32(E1000_CTRL);