dt-bindings: mfd: Add binding for qnap,ts433-mcu devices

dt-bindings: mfd: Add binding for qnap,ts433-mcu devices

These MCUs can be found in network attached storage devices made by QNAP.
They are connected to a serial port of the host device and provide
functionality like LEDs, power-control and temperature monitoring.

LEDs, buttons, etc are all elements of the MCU firmware itself, so don't
need devicetree input, though the fan gets its cooling settings from
a fan-0 subnode.

A binding for the LEDs for setting the linux-default-trigger may come
later, once all the LEDs are understood and ATA controllers actually
can address individual port-LEDs, but are really optional.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20241107114712.538976-4-heiko@sntech.de
Signed-off-by: Lee Jones <lee@kernel.org>