USB: add SPDX identifiers to all remaining Makefiles

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 <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Peter Korsgaard <jacmet@sunsite.dk>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Cc: Johan Hovold <johan@kernel.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/c67x00/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for Cypress C67X00 USB Controller
 #

drivers/usb/class/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for USB Class drivers
 # (one step up from the misc category)

drivers/usb/early/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for early USB devices
 #

drivers/usb/image/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for USB Image drivers
 #

drivers/usb/isp1760/Makefile

+# SPDX-License-Identifier: GPL-2.0
 isp1760-y := isp1760-core.o isp1760-if.o
 isp1760-$(CONFIG_USB_ISP1760_HCD) += isp1760-hcd.o
 isp1760-$(CONFIG_USB_ISP1761_UDC) += isp1760-udc.o

drivers/usb/misc/sisusbvga/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for the sisusb driver (if driver is inside kernel tree).
 #

drivers/usb/mon/Makefile

+# SPDX-License-Identifier: GPL-2.0
 #
 # Makefile for USB monitor
 #

drivers/usb/serial/Makefile-keyspan_pda_fw

+# SPDX-License-Identifier: GPL-2.0
 
 # some rules to handle the quirks of the 'as31' assembler, like
 # insisting upon fixed suffixes for the input and output files,

drivers/usb/typec/Makefile

+# SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_TYPEC)		+= typec.o
 obj-$(CONFIG_TYPEC_TCPM)	+= tcpm.o
 obj-y				+= fusb302/

drivers/usb/typec/fusb302/Makefile

+# SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_TYPEC_FUSB302)	+= fusb302.o