ASoC: Add initial WM8962 CODEC driver

The WM8962 is a low power, high performance stereo CODEC designed for
portable digital audio applications.

This initial driver release supports the key audio paths of the WM8962.
Extended functionality, such as microphone detection, digital microphones
and the advanced DSP signal enhancements provided by the device are not
yet supported.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>