iio: add Capella CM32181 ambient light sensor driver.

Add Capella Microsystem CM32181 Ambient Light Sensor IIO driver.
This driver will convert raw data to lux value under open-air
condition. Change the calibscale based on the cover material.

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

diff --cc Documentation/devicetree/bindings/i2c/trivial-devices.txt
Simple merge

diff --cc drivers/iio/light/Kconfig
Simple merge

diff --cc drivers/iio/light/Makefile
Simple merge

diff --cc drivers/iio/light/cm32181.c
Simple merge