tools lib traceevent: Add offset option for function plugin

When the offset option is set for the function plugin enabled, it will
display the offset of the functions along with their names.  This helps
in finding exactly where a function was called by its parent.

  trace-cmd report -O parent -O offset
 [..]
        rcuc/163-1330  [163]   740.653251: function: _raw_spin_lock+0x0  <-- rcu_cpu_kthread+0x4d8

Link: http://lore.kernel.org/linux-trace-devel/20200702174950.123454-2-tz.stoyanov@gmail.com



Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[ Ported from trace-cmd.git ]
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/lkml/20200702185704.986181512@goodmis.org


Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>