ppc_oldworld, ppc_newworld: fix escc BAR related crash ppc maps the escc mmio region both at a fixed offset (as a sysbus area) and as part of a PCI BAR. This crashes, since a MemoryRegion may have only one parent. Use an alias so we have a separate MemoryRegion for the BAR. Signed-off-by: Avi Kivity <avi@redhat.com>