V4L/DVB (3661): Add wm8739 stereo audio ADC i2c driver

Add support for the Wolfson Microelectronics WM8739
stereo A/D converter from the ivtv driver.
Many thanks to Takahiro Adachi for writing the original driver.

Signed-off-by: Takahiro Adachi <tadachi@tadachi-net.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>