egl-helpers: Change file licensing to LGPLv2

The relicense permits sharing the code with Spice which
is LGPL.

All people listed below have agreed to the
relicense:
- Arei Gonglei;
- Cole Robinson;
- Gerd Hoffmann;
- Peter Maydell.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Cole Robinson <crobinso@redhat.com>
Acked-by: Gonglei <arei.gonglei@huawei.com>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20161208104539.3045-1-fziglio@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>