tools lib traceevent: Move kernel_stack event handler to "function" plugin.

tools lib traceevent: Move kernel_stack event handler to "function" plugin.

The "kernel_stack" event handler does not depend on any trace-cmd
context, it can be used aside from the application. The code is moved to
libtraceevent "function" plugin.

Link: http://lore.kernel.org/linux-trace-devel/20190726124308.18735-2-tz.stoyanov@gmail.com
Link: http://lore.kernel.org/linux-trace-devel/20200702174950.123454-4-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/20200702185705.284789930@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>