rockchip: Add an I2S driver

Add a driver for I2S which allows audio data to be sent from the SoC to
the audio codec. The sample rate and other settings are hard-coded for now
as there is no suitable device-tree binding available.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/drivers/sound/Kconfig b/drivers/sound/Kconfig
index c0d97cc..22e3796 100644
--- a/drivers/sound/Kconfig
+++ b/drivers/sound/Kconfig
@@ -21,6 +21,15 @@
 	  I2S. It calls either of the two supported codecs (no use is made
 	  of driver model at present).
 
+config I2S_ROCKCHIP
+	bool "Enable I2S support for Rockchip SoCs"
+	depends on I2S
+	help
+	  Rockchip 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. This driver does not make use of
+	  DMA, but writes each word directly to the hardware.
+
 config I2S_SAMSUNG
 	bool "Enable I2C support for Samsung SoCs"
 	depends on SOUND