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/drivers/sound/Kconfig b/drivers/sound/Kconfig
index 759a10f..1b97af0 100644
--- a/drivers/sound/Kconfig
+++ b/drivers/sound/Kconfig
@@ -18,3 +18,13 @@
 	  SoC to the audio codec. This option enables sound support using
 	  I2S. It calls either of the two supported codecs (no use is made
 	  of driver model at present).
+
+config I2S_SAMSUNG
+	bool "Enable I2C support for Samsung SoCs"
+	depends on SOUND
+	help
+	  Samsung Exynos SoCs support an I2S interface for sending audio
+	  data to an audio codec. This option enables support for this,
+	  using one of the available audio codec drivers. Enabling this
+	  option provides an implementation for sound_init() and
+	  sound_play().