dt-bindings: input: Convert Pixcir Touchscreen binding to a schema

The Pixcir Touchscreen Controller is supported by Linux thanks to
its 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.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210721140424.725744-18-maxime@cerno.tech


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>