arm64: rockchip: add hdmi audio rock pi

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>

arch/arm64/boot/dts/rockchip/rk3399-rock-pi-4.dts

@@ -169,6 +169,10 @@
 	status = "okay";
 };
 
+&hdmi_sound {
+	status = "okay";
+};
+
 &i2c0 {
 	clock-frequency = <400000>;
 	i2c-scl-rising-time-ns = <168>;