arm64: dts: mediatek: Add MT6331 PMIC devicetree

MT6331 is the primary PMIC for the MediaTek Helio X10 MT6795 smartphone
platforms: add a devicetree describing its regulators, Real Time Clock
and PMIC-keys.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20230412112739.160376-24-angelogioacchino.delregno@collabora.com


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