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/configs/snow_defconfig b/configs/snow_defconfig
index 0fd084b..6c76f4d 100644
--- a/configs/snow_defconfig
+++ b/configs/snow_defconfig
@@ -12,3 +12,4 @@
 CONFIG_I2S=y
 CONFIG_I2S_SAMSUNG=y
 CONFIG_SOUND_MAX98095=y
+CONFIG_SOUND_WM8994=y