[ALSA] ASoC: Add WM8990 driver

The WM8990 is a highly integrated ultra-low power hi-fi codec designed
for handsets rich in multimedia features such as mobile TV, digital
audio playback and gaming.

The bulk of this driver was written by Liam Girdwood with some
additional development and updates for new ASoC APIs by me.

Signed-off-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>