tools lib traceevent: Change to SPDX License format

Replace the GPL text with SPDX tags in the tools/lib/traceevent files.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Cc: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lkml.kernel.org/r/20180816111015.125e0f25@gandalf.local.home


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>