hw/pci-host/bonito.c: Add PCI mem region mapped at the correct address

hw/pci-host/bonito.c: Add PCI mem region mapped at the correct address

Stop using system memory as PCI memory otherwise devices such as VGA
that have regions mapped to PCI memory clash with RAM. Use a separate
memory region for PCI memory and map it to the correct address in
system memory which allows PCI mem regions to show at the correct
address where clients expect them.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>