sandbox: exynos: Move CONFIG_SOUND 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 6417a77..6b2c8bd 100644
--- a/configs/snow_defconfig
+++ b/configs/snow_defconfig
@@ -7,3 +7,4 @@
 CONFIG_CROS_EC_I2C=y
 CONFIG_CROS_EC_KEYB=y
 CONFIG_CMD_CROS_EC=y
+CONFIG_SOUND=y