mfd/pinctrl/regulator: Add RK806 Support

Merge series from Sebastian Reichel <sebastian.reichel@collabora.com>:

All existing boards using RK3588/RK3588s use RK806 PMICs. This series is now
the main blocker for full upstream support of those boards and it would be good
to have it merged for 6.5 :) The patches have been tested on multiple different
platforms and are mainly missing an Ack from Mark or Liam for the rk808-regulator
changes.

Merging must happen through a single tree, since the pinctrl and regulator
drivers rely on the register definitions from the include file added by the MFD
patch. My suggested merge strategy is that Lee creates an immutable branch for
the regulator/pinctrl tree once all Acks have been collected.