usb: New usb_new(), usb_realize_and_unref()

I'm converting from qdev_create()/qdev_init_nofail() to
qdev_new()/qdev_realize_and_unref(); recent commit "qdev: New
qdev_new(), qdev_realize(), etc." explains why.

USB devices use qdev_create() through usb_create().

Provide usb_new() and usb_realize_and_unref() for converting USB
devices.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200610053247.1583243-27-armbru@redhat.com>

hw/usb/bus.c

@@ -314,6 +314,16 @@ void usb_legacy_register(const char *typename, const char *usbdevice_name,
     }
 }
 
+USBDevice *usb_new(const char *name)
+{
+    return USB_DEVICE(qdev_new(name));
+}
+
+bool usb_realize_and_unref(USBDevice *dev, USBBus *bus, Error **errp)
+{
+    return qdev_realize_and_unref(&dev->qdev, &bus->qbus, errp);
+}
+
 USBDevice *usb_create(USBBus *bus, const char *name)
 {
     DeviceState *dev;

include/hw/usb.h

@@ -504,6 +504,8 @@ USBBus *usb_bus_find(int busnr);
 void usb_legacy_register(const char *typename, const char *usbdevice_name,
                          USBDevice *(*usbdevice_init)(USBBus *bus,
                                                       const char *params));
+USBDevice *usb_new(const char *name);
+bool usb_realize_and_unref(USBDevice *dev, USBBus *bus, Error **errp);
 USBDevice *usb_create(USBBus *bus, const char *name);
 USBDevice *usb_create_simple(USBBus *bus, const char *name);
 USBDevice *usbdevice_create(const char *cmdline);