soc: mediatek: Introduce mediatek-regulator-coupler driver

This driver currently deals with GPU-SRAM regulator coupling, ensuring
that the SRAM voltage is always between a specific range of distance to
the GPU voltage, depending on the SoC, necessary in order to achieve
system stability across the full range of supported GPU frequencies.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Link: https://lore.kernel.org/r/20221006115816.66853-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>