add license

/*!

 * @section LICENSE

 * $license_gpl$

 * (C) Copyright 2011~2015 Bosch Sensortec GmbH All Rights Reserved

 *

 * @filename $filename$

 * @date     2016/04/21 14:40

 * @id       $id$

 * This software program is licensed subject to the GNU General

 * Public License (GPL).Version 2,June 1991,

 * available at http://www.fsf.org/copyleft/gpl.html

 *

 * @filename bmi160_core.c

 * @date     2015/11/17 14:40

 * @id       "128af5d"

 * @version  1.2

 *

 * @brief