devantech-srf04.yaml: transform DT binding to YAML

devantech-srf04.yaml: yaml devicetree binding for iio ultrasonic
proximity driver of devantech srf04

use devantech-srf04.txt, transform binding into yaml and remove the
outdated DT documentation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>