AK5558 is a 32-bit, 768 kHZ sampling, differential input ADC
for digital audio systems.

Datasheet is available at:

https://www.akm.com/akm/en/file/datasheet/AK5558VN.pdf

Initial patch includes support for normal and TDM modes.
Reviewed-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NJunichi Wakasugi <wakasugi.jb@om.asahi-kasei.co.jp>
[initial coding for 3.18 kernel]
Signed-off-by: NMihai Serban <mihai.serban@nxp.com>
[cleanups and porting to 4.9 kernel]
Signed-off-by: NShengjiu Wang <shengjiu.wang@nxp.com>
[tdm support]
Signed-off-by: NDaniel Baluta <daniel.baluta@nxp.com>
[pm support, cleanups and porting to latest kernel]
Signed-off-by: NMark Brown <broonie@kernel.org>