scripts/Makefile* Add SPDX-License-Identifier tag

A general best practice for SPDX is that Makefiles should have an
identifier, add these as everything else is currently covered.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index ed30bf5..1644f8c 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -1,3 +1,6 @@
+#
+# SPDX-License-Identifier:	GPL-2.0
+#
 # Backward compatibility
 asflags-y  += $(EXTRA_AFLAGS)
 ccflags-y  += $(EXTRA_CFLAGS)