q800: move mac-nubus-bridge device to Q800MachineState

q800: move mac-nubus-bridge device to Q800MachineState

Also change the instantiation of the mac-nubus-bridge device to use
object_initialize_child() and map the Nubus address space using
memory_region_add_subregion() instead of sysbus_mmio_map().

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230621085353.113233-21-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>