ASoC: pcm179x: Add I2C interface driver

The PCM179x family supports both SPI and I2C. This patch adds support
for the I2C interface.

Signed-off-by: Jacob Siverskog <jacob@teenage.engineering>
Reviewed-by: Johan Hovold <johan@kernel.org>
Acked-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Mark Brown <broonie@kernel.org>