tracing: Add TRACE_EVENT_CONDITION sample

The sample code lacks an example of TRACE_EVENT_CONDITION, and it
has been expressed to me that this feature for TRACE_EVENT is not
well known and not used when it could be.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --cc samples/trace_events/trace-events-sample.c
Simple merge

diff --cc samples/trace_events/trace-events-sample.h
Simple merge