libtraceevent: Move traceevent plugins in its own subdirectory

All traceevent plugins code is moved to tools/lib/traceevent/plugins
subdirectory. It makes traceevent implementation in trace-cmd and in
kernel tree consistent. There is no changes in the way libtraceevent and
plugins are compiled and installed.

Committer notes:

Applied fixup provided by Steven, fixing the tools/perf/Makefile.perf
target for the plugin dynamic list file. Problem noticed when cross
building to aarch64 from a Ubuntu 19.04 container.

Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
Cc: linux-trace-devel@vger.kernel.org
Link: http://lore.kernel.org/lkml/20190923115929.453b68f1@oasis.local.home
Link: http://lore.kernel.org/lkml/20190919212542.377333393@goodmis.org
Link: http://lore.kernel.org/linux-trace-devel/20190917105055.18983-1-tz.stoyanov@gmail.com


Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>