regulator: mt6358: Add support for MT6358 regulator

The MT6358 is a regulator found on boards based on MediaTek MT8183 and
probably other SoCs. It is a so called pmic and connects as a slave to
SoC using SPI, wrapped inside the pmic-wrapper.

Signed-off-by: Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>
Link: https://lore.kernel.org/r/1566531931-9772-8-git-send-email-hsin-hsiung.wang@mediatek.com


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