dtc

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>