arm64: dts: rockchip: enable hdmi output on rk3399-rockpro64

The rockpro64 does have hdmi support, so add the necessary
devicetree node to enable it.
Signed-off-by: Oskari Lemmela <oskari@lemmela.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/boot/dts/rockchip/rk3399-rockpro64.dts

@@ -205,6 +205,13 @@ &gmac {
 	status = "okay";
 };
 
+&hdmi {
+	ddc-i2c-bus = <&i2c3>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&hdmi_cec>;
+	status = "okay";
+};
+
 &i2c0 {
 	clock-frequency = <400000>;
 	i2c-scl-rising-time-ns = <168>;