dt-bindings:iio:adc:envelope-detector: txt to yaml conversion.

Straight forward format conversion.  The example in here is fun in
that it has 2 separate provider / consumer pairs.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20201031181242.742301-5-jic23@kernel.org