arm64: dts: db820c: Add sound card support

This patch adds support both digital and analog audio on DB820c.
This board has HDMI port and 3.5mm audio jack to support both digital
and analog audio respectively.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Andy Gross <agross@kernel.org>