uboot-imx

sandbox: sound: Silence sound for testing

When testing the sound system we don't need the hear the beeps. The
testing works by checking the data that would be emitted. Add a
device-tree property to silence the sound, and enable it for testing.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>