dt-bindings: add parallax ping sensors

Add dt-bindings for parallax PING))) and LaserPING iio sensors, which
are used for measuring distances.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>