input: Add onkey driver for Marvell 88PM886 PMIC

Marvell 88PM886 PMIC provides onkey among other things. Add client
driver to handle it. The driver currently only provides a basic support
omitting additional functions found in the vendor version, such as long
onkey and GPIO integration.

Signed-off-by: Karel Balej <balejk@matfyz.cz>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20240531175109.15599-5-balejk@matfyz.cz


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