lttng instrumentation: tracepoint events

Modifications to the in-kernel TRACE_EVENT are needed to generate the
compact event descriptions and the probe code LTTng generates. These
changes could apply to upstream TRACE_EVENT, but requires changing the
in-kernel API.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>