arm64: dts: mediatek: Add ADC node on MT6357, MT6358, MT6359 PMICs

Add support for the ADC on MT6357/8/9 and keep it default enabled
as this IP is always present on those PMICs.
Users may use different IIO channels depending on board-specific
routing.

Link: https://lore.kernel.org/r/20240604123008.327424-6-angelogioacchino.delregno@collabora.com


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