experimental kernel-3.7 support

On 2013-01-24 17:47, Hans Verkuil wrote on linux-media@vger.kernel.org:
> In 3.7 the vfl_dir field was added to struct video_device. For output
> devices this has to be set to VFL_DIR_TX. For devices that do both
> capture and output it has to be set to VFL_DIR_M2M (memory-to-memory).
> Otherwise the v4l2 core will assume that it is a capture device and
> disable any output support.