host-tools: use python2 explicitly for shebang

All of these host tools are apparently written for Python2,
not Python3.

Use 'python2' in the shebang line according to PEP 394
(https://www.python.org/dev/peps/pep-0394/

).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

scripts/dtc/pylibfdt/setup.py

-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 """
 setup.py file for SWIG libfdt

scripts/mailmapper

-#!/usr/bin/env python
+#!/usr/bin/env python2
 #
 # Copyright (C) 2014, Masahiro Yamada <yamada.m@jp.panasonic.com>
 #

test/py/test.py

-#!/usr/bin/env python
+#!/usr/bin/env python2
 
 # Copyright (c) 2015 Stephen Warren
 # Copyright (c) 2015-2016, NVIDIA CORPORATION. All rights reserved.

tools/buildman/buildman.py

-#!/usr/bin/env python
+#!/usr/bin/env python2
 #
 # Copyright (c) 2012 The Chromium OS Authors.
 #

tools/dtoc/dtoc.py

-#!/usr/bin/python
+#!/usr/bin/env python2
 #
 # Copyright (C) 2016 Google, Inc
 # Written by Simon Glass <sjg@chromium.org>

tools/microcode-tool.py

-#!/usr/bin/env python
+#!/usr/bin/env python2
 #
 # Copyright (c) 2014 Google, Inc
 #

tools/patman/patman.py

-#!/usr/bin/env python
+#!/usr/bin/env python2
 #
 # Copyright (c) 2011 The Chromium OS Authors.
 #

tools/rkmux.py

-#!/usr/bin/python
+#!/usr/bin/env python2
 
 # Script to create enums from datasheet register tables
 #