dt-bindings:iio:proximity:semtech,sx9500 yaml conversion.

Simple conversion.  There hasn't been much activity around this driver
for a long time and I don't think I have any up to date contact details
for the original authors.  As such, I've listed myself as the binding
maintainer.  More than happy to hand it off to someone more relevant though!

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201031134110.724233-10-jic23@kernel.org