ASoC: Add ADAU1977 CODEC driver

This patch adds support for the ADAU1977, ADAU1978 and ADAU1979 audio CODEC
devices. They are a family of 4-channel differential input audio ADC devices.
They can be connected to either a SPI or I2C bus. The driver is implemented in
three modules, one main module (adau1977.ko) which implements the device logic
and one module each for SPI (adau1977-spi.ko) and I2C (adau1977-i2c.ko) bus
access.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>