ARM: dts: imx6: rdu2: Limit USBH1 to Full Speed

Cabling used to connect devices to USBH1 on RDU2 does not meet USB
spec cable quality and cable length requirements to operate at High
Speed, so limit the port to Full Speed only.
Reported-by: Chris Healy <cphealy@gmail.com>
Reviewed-by: Chris Healy <cphealy@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi

@@ -807,6 +807,7 @@ switchphy4: switchphy@4 {
 &usbh1 {
 	vbus-supply = <&reg_5p0v_main>;
 	disable-over-current;
+	maximum-speed = "full-speed";
 	status = "okay";
 };