arm64: dts: rockchip: add chosen node on rk3399-sapphire

In order to use earlycon, the stdout-path property needs to be set
in the chosen node.
Signed-off-by: Vicente Bergas <vicencb@gmail.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-sapphire.dtsi

@@ -11,6 +11,10 @@
 / {
 	compatible = "rockchip,rk3399-sapphire", "rockchip,rk3399";
 
+	chosen {
+		stdout-path = "serial2:1500000n8";
+	};
+
 	backlight: backlight {
 		compatible = "pwm-backlight";
 		brightness-levels = <