tracing/selftest: Add selftests to test trace_marker histogram triggers

Add a couple of tests that test the trace_marker histogram triggers.
One does a straight histogram test, the other will create a synthetic event
and test the latency between two different writes (using filters to
differentiate between them).

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>