gst1-libav: add license info

gst1-libav: add license info

Now that we use unbundled ffmpeg the licensing becomes much easier.
Relevant code is under ext/*, which according to COPYING and comments is
GPLv2+, except for ext/libswscale/gstffmpegscale.c which is LGPLv2+ -
however that's not built/used when using system ffmpeg.

The code under gst-libs/ is the bundled ffmpeg itself.

Tests are under LGPLv2+ as well but we don't build them since we
disabled gst-check support in the gstreamer1 package.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>