sun4u: expose fw_cfg and NVRAM on ebus PCI IO address space

To allow future changes to the sun4u PCI topology.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-By: Artyom Tarasenko <atar4qemu@gmail.com>
