Add functions to get and set the current state of the state machine,
add tracepoints there to trace state transitions.  Add support for
traceing the queue heads and transfer descriptors as we look at them.

Drop a few DPRINTFs and all DPRINTF_ST lines, they are obsolete now.

No change in behavior.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>