License unification

Unify some license headers to satisfy https://github.com/RIOT-OS/RIOT/pull/1181
```
$ ./dist/tools/licenses/check.sh
$ wc -l dist/tools/licenses/out/*lgpl*
 212 dist/tools/licenses/out/lgpl-short-riot
  30 dist/tools/licenses/out/lgplv2.1-v1
  33 dist/tools/licenses/out/lgplv2-short-v1
  25 dist/tools/licenses/out/lgplv2-short-v2
  11 dist/tools/licenses/out/lgplv2-short-v3
 311 total
$ head -1 dist/tools/licenses/out/lgpl-short-riot
boards/arduino-due/board.c
$ head -7 boards/arduino-due/board.c
/*
 * Copyright (C) 2014 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser General
 * Public License. See the file LICENSE in the top level directory for more
 * details.
 */

```