dt-bindings: input: Add bindings for Mediatek matrix keypad

This patch add devicetree bindings for Mediatek matrix keypad driver.

Signed-off-by: fengping.yu <fengping.yu@mediatek.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220303154302.252041-2-mkorpershoek@baylibre.com


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