tools lib traceevent: Add pevent_print_func_field() helper function

Add the pevent_print_func_field() that will look up a field that is
expected to be a function pointer, and it will print the function name
and offset of the address given by the field.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20131101215501.869542711@goodmis.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>