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/arch/arm/mach-tegra/tegra30/Makefile b/arch/arm/mach-tegra/tegra30/Makefile
index bc250de..d3d3b6e 100644
--- a/arch/arm/mach-tegra/tegra30/Makefile
+++ b/arch/arm/mach-tegra/tegra30/Makefile
@@ -1,17 +1,7 @@
 #
 # Copyright (c) 2010-2012, NVIDIA CORPORATION.  All rights reserved.
 #
-# This program is free software; you can redistribute it and/or modify it
-# under the terms and conditions of the GNU General Public License,
-# version 2, as published by the Free Software Foundation.
-#
-# This program is distributed in the hope it will be useful, but WITHOUT
-# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
-# more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# SPDX-License-Identifier:	GPL-2.0
 #
 
 obj-$(CONFIG_SPL_BUILD) += cpu.o