Add support MT6316/6363/MT6373 PMICs regulators

Add support MT6316/6363/MT6373 PMICs regulators

Merge series from AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>:

This series adds support for three new MediaTek PMICs: MT6316, MT6363
and MT6373 and their variants - used in board designs featuring the
MediaTek MT8196 Chromebook SoC, or the MT6991 Dimensity 9400 Smartphone
SoC.

In particular, MT6316 is a regulator, but the MT6363 and MT6373 PMICs
are multi-function devices, as they have and expose multiple sub-devices;
moreover, some of those also contain an interrupt controller, managing
internal IPs interrupts: for those, a chained interrupt handler is
registered, which parent is the SPMI controller itself.

This series adds support for all of the MT6316 regulator variants and
for MT6363, MT6373 SPMI PMICs and their interrupt controller.