hw/acpi: fix a DSDT table issue when a pxb is present.

PXBs do not support hotplug so they don't have a PCNT function.
Since the PXB's PCI root-bus is a child bus of bus 0, the
build_dsdt code will add a call to the corresponding PCNT function.

Fix this by skipping the PCNT call for the above case.
While at it skip also PCIe child buses.

Reported-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/i386/acpi-build.c

@@ -600,6 +600,10 @@ static void build_append_pci_bus_devices(Aml *parent_scope, PCIBus *bus,
         QLIST_FOREACH(sec, &bus->child, sibling) {
             int32_t devfn = sec->parent_dev->devfn;
 
+            if (pci_bus_is_root(sec) || pci_bus_is_express(sec)) {
+                continue;
+            }
+
             aml_append(method, aml_name("^S%.02X.PCNT", devfn));
         }
     }