ftrace: Use synchronize_rcu_tasks_rude() instead of ftrace_sync()

This commit replaces the schedule_on_each_cpu(ftrace_sync) instances
with synchronize_rcu_tasks_rude().

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
[ paulmck: Make Kconfig adjustments noted by kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>