[media] DocBook/demux.xml: Add the remaining data structures to the API spec

Still, there are a few ioctl's not documented:

Error: no ID for constraint linkend: DMX_GET_PES_PIDS.
Error: no ID for constraint linkend: DMX_GET_CAPS.
Error: no ID for constraint linkend: DMX_SET_SOURCE.
Error: no ID for constraint linkend: DMX_ADD_PID.
Error: no ID for constraint linkend: DMX_REMOVE_PID.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>