iio: vcnl4000: add support for VCNL4200

VCNL4200 is an integrated long distance (up to 1500mm) proximity and
ambient light sensor.

The support is very basic. There is no configuration of proximity and
ambient light sensing yet. Only the reading of both measured values is
done.

The reading of ambient light and proximity values is blocking. If you
request a new value too early, the driver waits for new value to be
ready.

Signed-off-by: Tomas Novotny <tomas@novotny.cz>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>