arm64: dts: mediatek: mt7981: add I2C controller

MT7981 has one on-SoC I2C controller that differs from recent Mediatek
blocks by having a different SLAVE_ADDR register offset (thus a custom
binding compatible string).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20240604063159.29216-1-zajec5@gmail.com


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