ASoC: tlv320aic31xx: add explicit support for tlv320dac31xx

tlv320dac31xx is a subset of tlv320aic31xx:
- it does not have MIC inputs and ADC, thus capture is not supported,
- it has analog inputs AIN1/AIN2 that can be mixed into output.

Although tlv320dac31xx does work with tlv320aic31xx driver, this setup
does register non-existent widgets and non-existent capture stream.
Thus userspace lists non-existent objects in user interfaces, an can
access these, causing operations with device registers that are
declared as "reserved" in tlv320dac31xx datasheet.

This patch fixes this situation by separating controls/widgets/routes
into common, aic31xx-specific, and dac31xx-specific parts. Only parts
that match actual hardware (as declared in "compatible" device tree
property) are registered.

Changes from v1:
- update device tree binding documentation,
- rebased on top of "ASoC: codec duplicated callback function goes to
  component on tlv320aic31xx" commit.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Mark Brown <broonie@kernel.org>