user_events: Add self-test for ftrace integration

Tests basic functionality of registering/deregistering, status and
writing data out via ftrace mechanisms within user_events.

Link: https://lkml.kernel.org/r/20220118204326.2169-8-beaub@linux.microsoft.com



Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>