uboot-imx

dm: sound: Create an option to use driver model for sound

The U-Boot sound system provides basic support for beeping. At present it
does not use driver model, but it needs to be converted. Add an option to
enable driver model for sound. For now it is not connected to anything.
Future work will add drivers which use this option. It will then be
removed once everything is converted.

Signed-off-by: Simon Glass <sjg@chromium.org>