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: NSimon Glass <sjg@chromium.org>

arch/Kconfig

@@ -116,6 +116,7 @@ config SANDBOX
 	imply VIRTIO_SANDBOX
 	imply VIRTIO_BLK
 	imply VIRTIO_NET
+	imply DM_SOUND
 
 config SH
 	bool "SuperH architecture"

drivers/sound/Kconfig

@@ -12,6 +12,12 @@ config SOUND
 	  audio codecs are called from the sound-i2s code. This could be
 	  converted to driver model.
 
+config DM_SOUND
+	bool "Use driver model for sound"
+	help
+	  Enable this option to use driver model for sound devices. This is a
+	  migration option and will be removed.
+
 config I2S
 	bool "Enable I2S support"
 	depends on SOUND