Using new lttng tracepoint API

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>
Export required symbols from lttng-tracepoint

Addons modules register tracepoints, and the register/unregister functions
needs to be exported for linux >= 3.15.

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>