hw/pci-host/i440fx: Extract the IGD passthrough host bridge device

We can use a i440FX without the IGD passthrough host bridge.
Extract it into a new file, 'hw/pci-host/xen_igd_pt.c'.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191209095002.32194-6-philmd@redhat.com>
Acked-by: Paul Durrant <paul@xen.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 740401b..0c36106 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -420,6 +420,7 @@
 F: hw/xen/
 F: hw/xenpv/
 F: hw/i386/xen/
+F: hw/pci-host/xen_igd_pt.c
 F: include/hw/block/dataplane/xen*
 F: include/hw/xen/
 F: include/sysemu/xen-mapcache.h