ARM: imx6sx: remove Atheros AR8031 PHY fixup

ARM: imx6sx: remove Atheros AR8031 PHY fixup

If this patch breaks your system, enable AT803X_PHY driver and add a PHY
node to the board device tree:

	phy-connection-type = "rgmii-txid"; (or rgmii-id)
	ethernet-phy@X {
		reg = <0xX>;

		qca,clk-out-frequency = <125000000>;

		vddio-supply = <&vddh>;

		vddio: vddio-regulator {
			regulator-name = "VDDIO";
			regulator-min-microvolt = <1800000>;
			regulator-max-microvolt = <1800000>;
		};

		vddh: vddh-regulator {
			regulator-name = "VDDH";
		};
	};

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>