regulator: axp20x: add support for the AXP717

The X-Powers AXP717 is a typical PMIC from X-Powers, featuring four
DC/DC converters and 15 LDOs, on the regulator side.

Describe the chip's voltage settings and switch registers, how the
voltages are encoded, and connect this to the MFD device via its
regulator ID.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Mark Brown <broonie@kernel.org>
Tested-by: Ryan Walklin <ryan@testtoast.com>
Link: https://lore.kernel.org/r/20240310010211.28653-5-andre.przywara@arm.com


Signed-off-by: Lee Jones <lee@kernel.org>