USB: add missing SPDX lines to Kconfig and Makefiles

There are a few remaining drivers/usb/ files that do not have SPDX
identifiers in them, all of these are either Kconfig or Makefiles.  Add
the correct GPL-2.0 identifier to them to make scanning tools happy.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index 70e6c95..e4b2741 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 #
 # USB device configuration
 #