ftrace: Use the rcu _notrace variants for rcu_dereference_raw() and friends

As rcu_dereference_raw() under RCU debug config options can add quite a
bit of checks, and that tracing uses rcu_dereference_raw(), these checks
happen with the function tracer. The function tracer also happens to trace
these debug checks too. This added overhead can livelock the system.

Have the function tracer use the new RCU _notrace equivalents that do
not do the debug checks for RCU.

Link: http://lkml.kernel.org/r/20130528184209.467603904@goodmis.org
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>