iio: Added Capella cm3232 ambient light sensor driver.

CM3232 is an advanced ambient light sensor with I2C protocol interface.
The I2C slave address is internally hardwired as 0x10 (7-bit).  Writing
to configure register is byte mode, but reading ALS register requests to
use word mode for 16-bit resolution.

Signed-off-by: Kevin Tsai <ktsai@capellamicro.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>