dt-bindings: input: touchscreen: goodix: Add binding for GT9286 IC

Support for this chip is being added to the goodix driver: add the
DT binding for it.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Link: https://lore.kernel.org/r/20210109135512.149032-3-angelogioacchino.delregno@somainline.org


Reviewed-by: Bastien Nocera <hadess@hadess.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>