regulator: Add FP9931/JD9930

Merge series from Andreas Kemnade <andreas@kemnade.info>:

Add a driver for the FP9931/JD9930 regulator which provides the
comparatively high voltages needed for electronic paper displays.

Datasheet for the FP9931 is at
https://www.fitipower.com/dl/file/flXa6hIchVeu0W3K

Although it is in English, it seems to be only downloadable
from the Chinese part of that website.
For the JD9930 there can be a datasheet found at
https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/JD9930_2D00_0.7_2D00_JUN_2D00_2019.pdf

To simplify things, include the hwmon part directly which is only
one register read and there are not other functions besides
regulators in this chip.

diff --cc MAINTAINERS
Simple merge

diff --cc drivers/gpio/gpiolib.c
Simple merge

diff --cc drivers/regulator/Kconfig
Simple merge

diff --cc drivers/regulator/Makefile
Simple merge