We now only allow per port preallocated buffers. We exchange the index
into the array instead of passing the buffers around. We still use the
refcount to track when a buffer can be reused.
Improve API a little, allow passing the node as the first argument of
the interface call.
Implement alloc_buffer in v4l2 and improve the test.
Keep state variable to enumerate things. This allows us to remove the
expectation that the same index will give the same item.
Use a new rectangle type for video size. When enumerating sizes, this
allows us to specify relations between width and height more easily.
Remove the struct and bytes type, they are like pointer.
Add filter to enum_formats to speed up enumerations.
