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/lib/bzip2/Makefile b/lib/bzip2/Makefile
index 929c24e..f0b81ad 100644
--- a/lib/bzip2/Makefile
+++ b/lib/bzip2/Makefile
@@ -1,2 +1,6 @@
+#
+# SPDX-License-Identifier:	GPL-2.0+
+#
+
 obj-y += bzlib.o bzlib_crctable.o bzlib_decompress.o \
 	bzlib_randtable.o bzlib_huffman.o