ARM: dts: microsom-ar8035: MDIO pad must be set open drain

This patch is important for the MicroSOM implementation due to the
following details -

1. VIH of the Atheros phy is 1.7V.
2. NVCC_ENET which is the power domain of the MDIO pad is driven by the
   PHY's LDO (i.e. either 1.8v or 2.5v).
3. The MicroSOM implements an onbouard 1.6kohm pull up to 3.3v (R3000).

In the case the PHY's LDO was 1.8v then there would be only a 100mV
margin for the signal to be acknowledged as high (1.8v-1.7v).
Due to that setting the pad as an open drain will let the 1.6kohm pull
that signal high to 3.3 that assures enough margins to the PHY to be
acked as '1' logic.
Signed-off-by: Rabeeh Khoury <rabeeh@solid-run.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/boot/dts/imx6qdl-microsom-ar8035.dtsi

@@ -17,7 +17,7 @@ &iomuxc {
 	enet {
 		pinctrl_microsom_enet_ar8035: microsom-enet-ar8035 {
 			fsl,pins = <
-				MX6QDL_PAD_ENET_MDIO__ENET_MDIO		0x1b0b0
+				MX6QDL_PAD_ENET_MDIO__ENET_MDIO		0x1b8b0
 				MX6QDL_PAD_ENET_MDC__ENET_MDC		0x1b0b0
 				/* AR8035 reset */
 				MX6QDL_PAD_KEY_ROW4__GPIO4_IO15		0x130b0