ASoC: add driver for Rockchip RK3xxx I2S controller

Add driver for i2s controller found on rk3066, rk3168 and rk3288
processors from rockchip.

Tested on the RK3288 SDK board.

Signed-off-by: Jianqun Xu <xjq@rock-chips.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/sound/soc/Kconfig b/sound/soc/Kconfig
index 0060b31..0e96233 100644
--- a/sound/soc/Kconfig
+++ b/sound/soc/Kconfig
@@ -47,6 +47,7 @@
 source "sound/soc/intel/Kconfig"
 source "sound/soc/mxs/Kconfig"
 source "sound/soc/pxa/Kconfig"
+source "sound/soc/rockchip/Kconfig"
 source "sound/soc/samsung/Kconfig"
 source "sound/soc/s6000/Kconfig"
 source "sound/soc/sh/Kconfig"