ASoC: tlv320adc3xxx: Add IIR filter configuration

The TLV320ADC3001/3101 have an internal DSP, which can either be
used in various preset configurations (called "Processing Blocks"
in the data sheet), or as a freely programmable (using the
"PurePath Studio" graphical programming tool from TI) but rather
small DSP ("miniDSP").

Using the default configuration (PRB_R1) it's possible to set up
filtering using a first-order IIR, which can be useful for adding
a digital high pass filter to the signal chain, for instance.

This patch adds support for configuring the IIR filter coefficients.
The filter itself is always enabled; the default coefficients
implement a pass-through function.

Signed-off-by: Ricard Wanderlof <ricardw@axis.com>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2202101805360.7068@lnxricardw1.se.axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>