Some kernels program a 0 address for io regions. PCI 3.0 spec
section 6.2.5.1 doesn't seem to disallow this.

based on patch by Michael Roth <mdroth@linux.vnet.ibm.com>

Add pci_allow_0_addr in MachineClass to conditionally
allow addr 0 for pseries, as this can break other architectures.

This patch allows to hotplug PCI card in pseries machine, as the first
added card BAR0 is always set to 0 address.

This as a temporary hack, waiting to fix PCI memory priorities for more
machine types...
Signed-off-by: NLaurent Vivier <lvivier@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>