tools lib traceevent: Optimize pretty_print() function

tools lib traceevent: Optimize pretty_print() function

Each time the pretty_print() function is called to print an event, the
event's format string is parsed. As this format string does not change,
this parsing can be done only once - when the event struct is
initialized.

Link: https://lore.kernel.org/linux-trace-devel/20200529134929.537110-1-tz.stoyanov@gmail.com
Link: http://lore.kernel.org/linux-trace-devel/20200625100516.365338-8-tz.stoyanov@gmail.com
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: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/lkml/20200702185704.559785000@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>