regulator: Updates for v4.20

This has been a very busy release for the core, some fixes, one large new
feature and a big bit of refactoring to update the GPIO API:

 - Support for coupled regulators from Dmitry Osipenko based on a prior
   attempt by Maciej Purski, allowing us to handle situations where the
   voltages on two regulators can't be too far apart from each other.
 - Conversion of the GPIO support in both drivers and the core to use
   GPIO descriptors rather than numbers, part of the overall project to
   remove GPIO numbers.
 - Support for standby mode suspend states from Andrei Stefanescu.
 - New drivers for Allwinner AXP209, Cirrus Logic Lochnagar and
   Microchip MPC16502.
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Merge remote-tracking branch 'regulator/topic/coupled' into regulator-next