iio:light: Add support for STMicro VL6180 sensor

This patch adds support for STMicro VL6180 - ALS, range and proximity sensor. Sensor is capable of measuring the light
intensity as well as object distance using TOF (Time of Flight) technology.

Signed-off-by: Manivannan Sadhasivam <manivannanece23@gmail.com>
Signed-off-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>