ASoC: pcm186x: Add initial PCM1862/63/64/65 universal ADC driver

This is an initial version of the PCM186x codec driver supporting both
2-channel and 4-channel device variants. Not all device features are
supported yet such as master/slave mode PLL configuration for which the
codec driver currently relies on the PCM186x built-in clock
auto-detection feature or the connection of digital microphones.
However here is what's here and what should work:

- Support for SPI and I2C low-level interfaces
- Regmap support and basic register definitions
- Input Mixer and Mux selection
- I2C, LJ, and TDM DAI format support

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Michael Stecklein <m-stecklein@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>