Work on memory allocation

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.

doc/design.txt

@@ -395,44 +395,46 @@ communication channel
 
    node-update
    port-update
-   start-configure
+   state-configure
 
 2) Set formats S->C                   CONFIGURE
 
-   add-port
    set-property
    enumerate ports
+   add-port
+   remove-port
    enumerate formats
    set-format
-   end-configure
 
-3) Buffer requirements update C->S    BUFFER_REQS
+3) Buffer requirements update C->S
 
    Update port status
-   start-alloc
+   state-ready if enough formats are set
 
-4) Start S->C                         ALLOC
+4) Start S->C                         READY
 
    read port memory requirements
    add_mem
+   remove_mem
    add_buffer
-   pause/start
+   remove_buffer
+   start->streaming
 
-5) Pause S->C                         PAUSED
+5) Pause S->C                         STREAMING
 
-   start/stop
+   stop-streaming
 
-5) data transfer C->S                 STARTED
+5) data transfer C->S
 
    need-input
+   have-output
+
    add_mem
    add_buffer
    process_buffer
    reuse_buffer
    remove_buffer
    remove_mem
-   have-output
-   pause/stop
 
 6) data transfer S->C
 
@@ -442,23 +444,17 @@ communication channel
    reuse_buffer
    remove_buffer
    remove_mem
-   pause/stop
 
 7) format change C->S
 
    port-update
-   start-configure
+   state-configure
 
 8) format change S->C
 
-   Send set-format change on ports
-   end-configure, back to 3
+   Send set-format change on ports -> READY if new memory requirements
+                                   -> RUNNING if all ok
 
-9) stop S->C                         ALLOC
+9) format-change to NULL  -> CONFIGURE
 
-   remove_buffer
-   remove_mem
-
-10) clear format S->C                 CONFIGURE
-
-   format-change to NULL
+10) ERROR