package/x264: disable optional ffmpeg support

package/x264: disable optional ffmpeg support

In buildroot ffmpeg uses x264 as optional dependency if
BR2_PACKAGE_FFMPEG_GPL is enabled at the same time.

If BR2_PACKAGE_FFMPEG_GPL is disabled and ffmpeg is built without x264
support before x264 itself is build, x264 picks up certain ffmpeg libs
as optional dependency leading to build errors because x264 does not
correctly link statically against ffmpeg.

To avoid a circular dependency and to avoid teaching x264 how to
correctly link statically with ffmpeg we just disable all ffmpeg-
related options.

Fixes
http://autobuild.buildroot.net/results/36a/36abb5b8f3aab57fb7b63056b216b4a58143ee3e/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>