ARM: dts: imx6: RIoTboard Add chosen stdout-path property

The RIoTboard debug uart is connected to serial1.
Add a chosen property in the DTS so OS knows what serial port to use for
the console.
Signed-off-by: Emmanuel Vadot <manu@freebsd.org>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6dl-riotboard.dts

@@ -19,6 +19,10 @@ memory@10000000 {
 		reg = <0x10000000 0x40000000>;
 	};
 
+	chosen {
+		stdout-path = "serial1:115200n8";
+	};
+
 	leds {
 		compatible = "gpio-leds";
 		pinctrl-names = "default";