ALSA: ASoC: Add WM8903 CODEC driver

The WM8903 is a high performance ultra-low power stereo CODEC optimised
for portable audio applications.  Features include:

    * 5mW power consumption for DAC to headphone playback
    * Stereo DAC SNR 96dB typical, THD -86dB typical
    * Stereo ADC SNR 93dB typical, THD -80dB typical
    * Up to 3 single ended inputs per stereo channel
    * Up to 2 pseudo differential inputs per stereo channel
    * Up to 1 fully differential mic input per stereo channel
    * Digital Dynamic Range Controller (compressor/limiter)
    * Digital sidetone mixing

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>