arm64: dts: mediatek: add per-SoC compatibles for keypad nodes

The mt6779-keypad binding specifies using a compatible for the
actual SoC before the generic MT6779 one.

Fixes: a8013418 ("arm64: dts: mediatek: mt8183: add keyboard node")
Fixes: 6ff94537 ("arm64: dts: mediatek: Initial mt8365-evk support")
Signed-off-by: Val Packett <val@packett.cool>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20241225192631.25017-3-val@packett.cool


Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>