arm64: dts: rockchip: enable analog audio node for rock64

The Rock64 boards has analog audio jack on it. RK3328 can output
analog audio signal using I2S1 and ACODEC core.

This patch adds sound node for analog audio for Rock64.

Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>