ASoC: hisilicon: Add hi6210 i2s audio driver

Add driver for hi6210 i2s controller found on hi6220 boards.

Signed-off-by: Andy Green <andy.green@linaro.org>
[jstultz: Forward ported to mainline, fairly major rework
 based on suggestions from Mark Brown]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>