Impact: new API, useful for tracepoints and markers.

Add _notrace version to rcu_read_*_sched().
Signed-off-by: NMathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Reviewed-by: NPaul E McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>