Implement new traceevent plugin API, which can be used to add new plugins
directories:

enum tep_plugin_load_priority {
	TEP_PLUGIN_FIRST,
	TEP_PLUGIN_LAST,
};

int tep_add_plugin_path(struct tep_handle *tep, char *path,
			enum tep_plugin_load_priority prio);

It adds the "path" as new plugin directory, in the context of the
handler "tep". The tep_load_plugins() API searches for plugins in this
new location. Depending of the priority "prio", the plugins from this
directory are loaded before (TEP_PLUGIN_FIRST) or after
(TEP_PLUGIN_LAST) the ordinary libtraceevent plugin locations.

Link: http://lore.kernel.org/linux-trace-devel/20191007114947.17104-2-tz.stoyanov@gmail.com
Link: http://lore.kernel.org/linux-trace-devel/20200625100516.365338-6-tz.stoyanov@gmail.comSigned-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/20200702185704.248123446@goodmis.orgSigned-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>