hw/pxb-pcie: fix PCI Express hotplug support

Add the missing osc method for pxb-pcie devices as APCI spec recommends,
see 6.2.9.1 OSC Implementation Example for PCI Host Bridge Devices, ACPI 3.0a:

    It is recommended that a machine with multiple host bridge devices
    should report the same capabilities for all host bridges, and also
    negotiate control of the features described in the Control Field in
    the same way for all host bridges.

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

dtc @ 65cc4d27

-Subproject commit ec02b34c05be04f249ffaaca4b666f5246877dea
+Subproject commit 65cc4d2748a2c2e6f27f1cf39e07a5dbabd80ebf

hw/i386/acpi-build.c

@@ -1962,6 +1962,9 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
             aml_append(dev, aml_name_decl("_UID", aml_int(bus_num)));
             aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0A03")));
             aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
+            if (pci_bus_is_express(bus)) {
+                aml_append(dev, build_q35_osc_method());
+            }
 
             if (numa_node != NUMA_NODE_UNASSIGNED) {
                 aml_append(dev, aml_name_decl("_PXM", aml_int(numa_node)));