dt-bindings: arm64: dts: mediatek: Add mt8183-pumpkin board

Add binding documentation for the MT8183 Pumpkin board.

Signed-off-by: Fabien Parent <fparent@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210217205945.830006-1-fparent@baylibre.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>