tools lib traceevent, perf tools: Rename struct event_format to struct tep_event_format

tools lib traceevent, perf tools: Rename struct event_format to struct tep_event_format

In order to make libtraceevent into a proper library, variables, data
structures and functions require a unique prefix to prevent name space
conflicts. That prefix will be "tep_". This renames struct event_format
to struct tep_event_format

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lkml.kernel.org/r/20180919185722.495820809@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>