trace: add tracetool simpletrace_stap format

trace: add tracetool simpletrace_stap format

This new tracetool "format" generates a SystemTap .stp file that outputs
simpletrace binary trace data.

In contrast to simpletrace or ftrace, SystemTap does not define its own
trace format.  All output from SystemTap is generated by .stp files.
This patch lets us generate a .stp file that outputs in the simpletrace
binary format.

This makes it possible to reuse simpletrace.py to analyze traces
recorded using SystemTap.  The simpletrace binary format is especially
useful for long-running traces like flight-recorder mode where string
formatting can be expensive.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>