usb core: use qdev for -usbdevice

This patchs adds infrastructure to handle -usbdevice via qdev callbacks.
USBDeviceInfo gets a name field (for the -usbdevice driver name) and a
callback for -usbdevice parameter parsing.

The new usbdevice_create() function walks the qdev driver list and looks
for a usb driver with a matching name.  When a parameter parsing
callback is present it is called, otherwise the device is created via
usb_create_simple().

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/hw/qdev.c b/hw/qdev.c
index 373ddfc..c7884d0 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -35,7 +35,7 @@
 /* This is a nasty hack to allow passing a NULL bus to qdev_create.  */
 static BusState *main_system_bus;
 
-static DeviceInfo *device_info_list;
+DeviceInfo *device_info_list;
 
 static BusState *qbus_find_recursive(BusState *bus, const char *name,
                                      const BusInfo *info);