dt-bindings: input: touchscreen: st1232: Convert to json-schema

Convert the Sitronix st1232/st1633 touchscreen controller Device Tree
binding documentation to json-schema.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Martin Kepplinger <martink@posteo.de>
Link: https://lore.kernel.org/r/fbba650cff07780c28ad6dd8dbef5cc1451b7762.1623418065.git.geert+renesas@glider.be
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>