sysbus: add sysbus_address_space()

Given a bus device, retrieves the memory address space for its bus.
Signed-off-by: NAvi Kivity <avi@redhat.com>

hw/sysbus.c

@@ -261,3 +261,8 @@ void sysbus_del_io(SysBusDevice *dev, MemoryRegion *mem)
 {
     memory_region_del_subregion(get_system_io(), mem);
 }
+
+MemoryRegion *sysbus_address_space(SysBusDevice *dev)
+{
+    return get_system_memory();
+}

hw/sysbus.h

@@ -57,6 +57,7 @@ void sysbus_del_memory(SysBusDevice *dev, MemoryRegion *mem);
 void sysbus_add_io(SysBusDevice *dev, target_phys_addr_t addr,
                    MemoryRegion *mem);
 void sysbus_del_io(SysBusDevice *dev, MemoryRegion *mem);
+MemoryRegion *sysbus_address_space(SysBusDevice *dev);
 
 /* Legacy helper function for creating devices.  */
 DeviceState *sysbus_create_varargs(const char *name,