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/arndale_defconfig b/configs/arndale_defconfig
index 3c0a6b3..3d5c870 100644
--- a/configs/arndale_defconfig
+++ b/configs/arndale_defconfig
@@ -6,3 +6,4 @@
 CONFIG_SOUND=y
 CONFIG_CMD_SOUND=y
 CONFIG_I2S=y
+CONFIG_I2S_SAMSUNG=y