dt-bindings: w1: Convert 1-Wire GPIO binding to a schema

Bitbanged 1-Wire buses are supported by Linux thanks to their device
tree binding.

Now that we have the DT validation in place, let's convert the device
tree bindings for that driver over to a YAML schema.

Cc: Daniel Mack <zonque@gmail.com>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210901091852.479202-39-maxime@cerno.tech
Signed-off-by: Rob Herring <robh@kernel.org>