iio: proximity: Add driver support for ST's VL53L0X ToF ranging sensor.

This driver was originally written by ST in 2016 as a misc input device
driver, and hasn't been maintained for a long time. I grabbed some code
from it's API and reformed it into an iio proximity device driver.
This version of driver uses i2c bus to talk to the sensor and
polling for measuring completes, so no irq line is needed.
It can be tested with reading from
/sys/bus/iio/devices/iio:deviceX/in_distance_input

Signed-off-by: Song Qiang <songqiang1304521@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>