mfd: Add driver for Marvell 88PM886 PMIC

Marvell 88PM886 is a PMIC which provides various functions such as
onkey, battery, charger and regulators. It is found for instance in the
samsung,coreprimevelte smartphone with which this was tested. Implement
basic support to allow for the use of regulators and onkey.

Signed-off-by: Karel Balej <balejk@matfyz.cz>
Link: https://lore.kernel.org/r/20240531175109.15599-3-balejk@matfyz.cz


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