ASOC: Add ADAU7118 8 Channel PDM-to-I2S/TDM Converter driver

This patch adds support for the 8 channel PDM-to-I2S/TDM converter. The
ADAU7118 converts four stereo pulse density modulation (PDM) bitstreams
into one pulse code modulation (PCM) output stream. The source for the PDM
data can be eight microphones or other PDM sources. The PCM audio data is
output on a serial audio interface port in either inter-IC serial (I2S) or
time domain multiplexed (TDM) format.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20191010074234.7344-1-nuno.sa@analog.com
Signed-off-by: Mark Brown <broonie@kernel.org>