In aic3x class of devices Output Common-Mode Voltage can be configured for
better analog performance.
The OCMV value depends on the Analog and digital domain power supply
voltage configuration.

The default OCMV of 1.35V gives best performance when AVDD is around 2.7V
and DVDD is 1.525V, but for higher AVDD/DVDD higher OCMV setting is
recommended.

The patch gives an automatic way of guessing the best OCMV which can be
overwritten by a DT parameter if needed.
Signed-off-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: NMark Brown <broonie@kernel.org>