dt-bindings: iio: srf04: add Maxbotix ultrasonic iio proximity sensors

add compatibles for Maxbotix ultrasonic iio sensor types to yaml
documentation

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>