Yesterday I committed the v4l support into the linuxulator (in 9-current). Part of this was the import of the v4l header from linux. We have the permission to use it, it is not licensed via GPL. This means we can use it in FreeBSD native drivers, and they are even allowed to be compiled into GENERIC (but I doubt we have a driver which could provide the v4l interface in GENERIC).
The code I committed is