Various Makefiles: Add SPDX-License-Identifier tags

After consulting with some of the SPDX team, the conclusion is that
Makefiles are worth adding SPDX-License-Identifier tags too, and most of
ours have one.  This adds tags to ones that lack them and converts a few
that had full (or in one case, very partial) license blobs into the
equivalent tag.

Cc: Kate Stewart <kstewart@linuxfoundation.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/usb/musb-new/Makefile b/drivers/usb/musb-new/Makefile
index fd9df72..072d516 100644
--- a/drivers/usb/musb-new/Makefile
+++ b/drivers/usb/musb-new/Makefile
@@ -1,6 +1,8 @@
 #
 # for USB OTG silicon based on Mentor Graphics INVENTRA designs
 #
+# SPDX-License-Identifier:	GPL-2.0+
+#
 
 obj-$(CONFIG_USB_MUSB_GADGET) += musb_gadget.o musb_gadget_ep0.o musb_core.o
 obj-$(CONFIG_USB_MUSB_GADGET) += musb_uboot.o