tracepoint: Support iterating over tracepoints on modules

Add for_each_module_tracepoint() for iterating over tracepoints
on modules. This is similar to the for_each_kernel_tracepoint()
but only for the tracepoints on modules (not including kernel
built-in tracepoints).

Link: https://lore.kernel.org/all/172397777800.286558.14554748203446214056.stgit@devnote2/



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