Add device-tree bindings for the keypad driver on the MT8183 Pumpkin
board.

The MT8183 Pumpkin board has 2 buttons connected using: KPROW0,
KPROW1 and KPCOL0.
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20220720-mt8183-keypad-v2-7-6d42c357cb76@baylibre.comSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>