ASoC: zx_aud96p22: add ZTE ZX AUD96P22 codec driver

It adds ASoC driver for AUD96P22 stereo audio codec integrated on ZTE
ZX family SoCs.  The driver includes the support for a number of volume
and mute controls, and power bits for various playback and recording
components.

Due to that the board for testing only supports playback, recording
support is untested.

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