V4L/DVB (5204): Change videodev2.h licence to dual GPL/BSD

videodev2.h contains just the V4L2 API structs and defines.
By allowing this header file to be dual GPL/BSD will enable sharing
userspace apps between Linux and *BSD systems. It will also allow developing
newer BSD licensed drivers that can be shared on Linux and *BSD.
It should be noticed that most of the current V4L drivers, and v4l core
itself are GPL only. This won't be changed by this patch.

Signed-off-by: Michael H. Schimek <mschimek@gmx.at>
Signed-off-by: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Bill Dirks <bill@thedirks.org>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Martin Rubli <mrubli@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>