regulator: Add driver for MT6331 PMIC regulators

Add a driver for the regulators found in the MT6331 PMIC.
This PMIC features six buck and 21 Low DropOut (LDO) regulators.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220913123456.384513-3-angelogioacchino.delregno@collabora.com


Signed-off-by: Mark Brown <broonie@kernel.org>