dt-bindings: input: Convert Silead GSL1680 binding to a schema

The Silead GSL1680 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.

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20211015073006.8939-1-maxime@cerno.tech


Signed-off-by: Rob Herring <robh@kernel.org>