ACPI: don't call acpi_pcihp_device_plug_cb on xen

Commit f0c9d64a exposed the issue that with a xenfv machine using
pci passthrough, acpi pci hotplug code was being executed by mistake.
Guard calls to acpi_pcihp_device_plug_cb (and corresponding
acpi_pcihp_device_unplug_cb) with a check for xen_enabled(). Without
this check I am seeing an error that the bus doesn't have the
acpi-pcihp-bsel property set.

Signed-off-by: Bruce Rogers <brogers@suse.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 153eba4726dfa1bdfc31d1fe973b2a61b9035492)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

hw/acpi/piix4.c

@@ -385,7 +385,10 @@ static void piix4_device_plug_cb(HotplugHandler *hotplug_dev,
                                 dev, errp);
         }
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
-        acpi_pcihp_device_plug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev, errp);
+        if (!xen_enabled()) {
+            acpi_pcihp_device_plug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev,
+                                      errp);
+        }
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
         if (s->cpu_hotplug_legacy) {
             legacy_acpi_cpu_plug_cb(hotplug_dev, &s->gpe_cpu, dev, errp);
@@ -408,8 +411,10 @@ static void piix4_device_unplug_request_cb(HotplugHandler *hotplug_dev,
         acpi_memory_unplug_request_cb(hotplug_dev, &s->acpi_memory_hotplug,
                                       dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
-        acpi_pcihp_device_unplug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev,
-                                    errp);
+        if (!xen_enabled()) {
+            acpi_pcihp_device_unplug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev,
+                                        errp);
+        }
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
                !s->cpu_hotplug_legacy) {
         acpi_cpu_unplug_request_cb(hotplug_dev, &s->cpuhp_state, dev, errp);