sandbox: exynos: Move CONFIG_I2S_SAMSUNG 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 eb8c64a..d8c01e6 100644
--- a/configs/snow_defconfig
+++ b/configs/snow_defconfig
@@ -10,3 +10,4 @@
 CONFIG_SOUND=y
 CONFIG_CMD_SOUND=y
 CONFIG_I2S=y
+CONFIG_I2S_SAMSUNG=y