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/ddr/fsl/Makefile b/drivers/ddr/fsl/Makefile
index df66c07..01ea862 100644
--- a/drivers/ddr/fsl/Makefile
+++ b/drivers/ddr/fsl/Makefile
@@ -1,9 +1,7 @@
 #
 # Copyright 2008-2014 Freescale Semiconductor, Inc.
 #
-# This program is free software; you can redistribute it and/or
-# modify it under the terms of the GNU General Public License
-# Version 2 as published by the Free Software Foundation.
+# SPDX-License-Identifier:	GPL-2.0
 #
 
 obj-$(CONFIG_SYS_FSL_DDR1) += main.o util.o ctrl_regs.o options.o \