[usb] Select preferred USB device configuration based on driver score

Generate a score for each possible USB device configuration based on
the available driver support, and select the configuration with the
highest score.  This will allow us to prefer ECM over RNDIS (for
devices which support both) and will allow us to meaningfully select a
configuration even when we have drivers available for all functions
(e.g. when exposing unused functions via EFI_USB_IO_PROTOCOL).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/smsc75xx.c

@@ -1052,6 +1052,7 @@ static struct usb_device_id smsc75xx_ids[] = {
 struct usb_driver smsc75xx_driver __usb_driver = {
 	.ids = smsc75xx_ids,
 	.id_count = ( sizeof ( smsc75xx_ids ) / sizeof ( smsc75xx_ids[0] ) ),
+	.score = USB_SCORE_NORMAL,
 	.probe = smsc75xx_probe,
 	.remove = smsc75xx_remove,
 };