ftrace: port to tracepoints

Porting the trace_mark() used by ftrace to tracepoints. (cleanup)

Changelog :
- Change error messages : marker -> tracepoint

[ mingo@elte.hu: conflict resolutions ]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Acked-by: 'Peter Zijlstra' <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>