sandbox: exynos: Move CONFIG_SOUND_WM8994 to Kconfig

Move this over to Kconfig and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/sound/Kconfig b/drivers/sound/Kconfig
index cfc75cb..a1c950b 100644
--- a/drivers/sound/Kconfig
+++ b/drivers/sound/Kconfig
@@ -36,3 +36,11 @@
 	  Enable the max98095 audio codec. This is connected via I2S for
 	  audio data and I2C for codec control. At present it only works
 	  with the Samsung I2S driver.
+
+config SOUND_WM8994
+	bool "Support Wolfson Micro wm8994 audio codec"
+	depends on I2S_SAMSUNG
+	help
+	  Enable the wm8994 audio codec. This is connected via I2S for
+	  audio data and I2C for codec control. At present it only works
+	  with the Samsung I2S driver.