regulator: Updates for v4.17

A very small set of updates for the regulator API this time around,
there's a few bug fixes and also:

 - Conversion of the regulator API to use GPIO descriptors rather than
   numbers from Linus Walleij.
 - New drivers for Marvell 88PG86x and Qualcomm PM8998 and PMI8998.
Merge remote-tracking branches 'regulator/topic/88pg86x', 'regulator/topic/dt', 'regulator/topic/formatting' and 'regulator/topic/gpio' into regulator-next