doc: Update information about resched_cpu

Since commit fced9c8cfe ("rcu: Avoid resched_cpu() when rescheduling
the current CPU"), resched_cpu is not directly called from
sync_sched_exp_handler. Update the documentation about the same.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

Documentation/RCU/Design/Expedited-Grace-Periods/Expedited-Grace-Periods.html

@@ -160,9 +160,9 @@ was in flight.
 If the CPU is idle, then <tt>sync_sched_exp_handler()</tt> reports
 the quiescent state.
 
-<p>
-Otherwise, the handler invokes <tt>resched_cpu()</tt>, which forces
-a future context switch.
+<p> Otherwise, the handler forces a future context switch by setting the
+NEED_RESCHED flag of the current task's thread flag and the CPU preempt
+counter.
 At the time of the context switch, the CPU reports the quiescent state.
 Should the CPU go offline first, it will report the quiescent state
 at that time.