dt-bindings: iio: adc: Add compatible for Mediatek MT8195

This commit adds dt-binding documentation of auxadc for Mediatek MT8195 SoC
Platform.

Signed-off-by: Seiya Wang <seiya.wang@mediatek.com>
Link: https://lore.kernel.org/r/20210319023427.16711-7-seiya.wang@mediatek.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>