ASoC: add bindings for ZTE zx-aud96p22 audio codec

It adds dt-bindings document for ZTE zx-aud96p22 audio codec.

Signed-off-by: Baoyou Xie <baoyou.xie@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>