dt-bindings: mfd: adp5585: ease on the required properties

It is not mandatory to use all the capabilities of the device. One can
very well only use it as a gpio controller without the PWM support. This
will be even more evident when support for the matrix keymap is added.
Hence drop the requirements for PWM and GPIO.

Acked-by: "Rob Herring (Arm)" <robh@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20250701-dev-adp5589-fw-v7-1-b1fcfe9e9826@analog.com
Signed-off-by: Lee Jones <lee@kernel.org>