ASoC: Add PCM1792A spi mode codec support

Add PCM1792A spi mode codec support. This version implements only
a subset of functionalities. Tested connect to a pandaboard ES
device and based on recently pcm1681 codec.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Mark Brown <broonie@linaro.org>