Rework transport protocol

Remove the old PinosBuffer object and replace it with SpaControl, this
communication protocol is designed to make it possible to implement
remote nodes and so it is moved to Spa.
Move SpaBuffer into to API
Work on easier API to make formats, implement enumeration and support
for all formats in v4l2.
Improve format output in -inspect

doc/design.txt

@@ -370,3 +370,95 @@ Types:
                      1 = keyframe+full headers
    <PTS>          : the timestamp when the refresh should be,
                      0 for as soon as possible
+
+
+
+communication channel
+---------------------
+
+
+               +-----+   +----+   +----+
+               |     |   |  S |   |    |
+               |     -----    -----    |
+               +-----+   +----+   +----+
+                           |
+                           |
+                           |
+                           |
+                         +----+
+                         |    |
+                         |  C |
+                         +----+
+
+
+1) Update config C->S                 INIT
+
+   node-update
+   port-update
+   start-configure
+
+2) Set formats S->C                   CONFIGURE
+
+   add-port
+   set-property
+   enumerate ports
+   enumerate formats
+   set-format
+   end-configure
+
+3) Buffer requirements update C->S    BUFFER_REQS
+
+   Update port status
+   start-alloc
+
+4) Start S->C                         ALLOC
+
+   read port memory requirements
+   add_mem
+   add_buffer
+   pause/start
+
+5) Pause S->C                         PAUSED
+
+   start/stop
+
+5) data transfer C->S                 STARTED
+
+   need-input
+   add_mem
+   add_buffer
+   process_buffer
+   reuse_buffer
+   remove_buffer
+   remove_mem
+   have-output
+   pause/stop
+
+6) data transfer S->C
+
+   add_mem
+   add_buffer
+   process_buffer
+   reuse_buffer
+   remove_buffer
+   remove_mem
+   pause/stop
+
+7) format change C->S
+
+   port-update
+   start-configure
+
+8) format change S->C
+
+   Send set-format change on ports
+   end-configure, back to 3
+
+9) stop S->C                         ALLOC
+
+   remove_buffer
+   remove_mem
+
+10) clear format S->C                 CONFIGURE
+
+   format-change to NULL