Make buffer data point to a registered memory block by its mem_id.
Add some more helpers to allocate memfd backed memory.
Allocate buffers in memfd so that we easily share them between client
and server.
Update pts and seq in v4l2 now that this change will actually be visible
at the client.
Use stucture offsets instead of pointers so that we can share the buffer
structure between client and server.
We can then pass an fd wrapping the memory of the buffer to the client.
Add beginnings of a memory pool
Rework things so that we negotiate buffer pools beforehand and only pass
buffer ids around We can then remove the refcount of buffers, events and
commands.
More work on buffer reuse
Use the node state changes to trigger the next step in the configuration
sequence.
Move most of the client-node to a plugin
Do buffer allocation in the port link.
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.
