soc: mediatek: mtk-pmic-wrap: Add support for companion PMICs

Some PMICs are designed to work with a companion part, which provides
more regulators and/or companion devices such as LED controllers,
display backlight controllers, battery charging, fuel gauge, etc:
this kind of PMICs are usually present in smartphone platforms, where
tight integration is required.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Link: https://lore.kernel.org/r/20230412131216.198313-5-angelogioacchino.delregno@collabora.com


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