It's good to have SPDX identifiers in all files to make it easier to
audit the kernel tree for correct licenses.

This updates the remaining drivers/usb/*Makefile* that were missing SPDX
identifiers. They all get the following identifier:
SPDX-License-Identifier: GPL-2.0

The SPDX identifier is a legally binding shorthand, which can be used
instead of the full boiler plate text.

Cc: Thomas Gleixner
Cc: Kate Stewart
Cc: Philippe Ombredanne
Cc: Peter Korsgaard
Cc: Thomas Winischhofer
Cc: Johan Hovold
Acked-by: Heikki Krogerus
Signed-off-by: Greg Kroah-Hartman