tlv320aic23 chip control interface may work in either I2C or SPI mode
depending on the MODE pin state. Functionality and register layout are
independent of the control mode.

Implement bus-specific parts as separate modules.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NMark Brown <broonie@linaro.org>