tracing: tprobe-events: Register tracepoint when enable tprobe event

As same as fprobe, register tracepoint stub function only when enabling
tprobe events. The major changes are introducing a list of
tracepoint_user and its lock, and tprobe_event_module_nb, which is
another module notifier for module loading/unloading.  By spliting the
lock from event_mutex and a module notifier for trace_fprobe, it
solved AB-BA lock dependency issue between event_mutex and
tracepoint_module_list_mutex.

Link: https://lore.kernel.org/all/174343538901.843280.423773753642677941.stgit@devnote2/



Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>