libfdt: Add dual GPL/BSD SPDX tags to files missing license text

A couple of libfdt files are missing licenses. Add (GPL-2.0-or-later OR
BSD-2-Clause) SPDX tag to them.

Signed-off-by: Rob Herring <robh@kernel.org>
Message-Id: <20190620211944.9378-6-robh@kernel.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/Makefile.libfdt

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause)
 # Makefile.libfdt
 #
 # This is not a complete Makefile of itself.  Instead, it is designed to

libfdt/version.lds

@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: (GPL-2.0-or-later OR BSD-2-Clause) */
 LIBFDT_1.2 {
 	global:
 		fdt_next_node;