rcu: Add a trace event for synchronize_rcu_normal()

rcu: Add a trace event for synchronize_rcu_normal()

Add an rcu_sr_normal() trace event. It takes three arguments
first one is the name of RCU flavour, second one is a user id
which triggeres synchronize_rcu_normal() and last one is an
event.

There are two traces in the synchronize_rcu_normal(). On entry,
when a new request is registered and on exit point when request
is completed.

Please note, CONFIG_RCU_TRACE=y is required to activate traces.

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>