ASoC: AD1836: Add AD1835/AD1837/AD1838/AD1839 support

The AD183X codec devices are mostly register compatible and can easily be
supported by the same driver.  The main difference between those devices
is the number of DACs and ADCs.

This patch adjusts the driver to allocate the controls, DAPM widgets and
routes for the DACs and ADCs dynamically based on the chip type.

The AD1836 is a bit special in that it supports different modes for its second
ADC, so it needs some special handling. Right now the driver hardcodes the mode
to the differential PGA mode.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>