tools lib traceevent: Man page for get/set cpus APIs

tools lib traceevent: Man page for get/set cpus APIs

Create man pages for libtraceevent APIs:

 tep_get_cpus(),
 tep_set_cpus()

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/linux-trace-devel/20190503091119.23399-6-tstoyanov@vmware.com
Link: http://lkml.kernel.org/r/20190510200106.742948683@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>