rcu: Merge rcu_sched_force_quiescent_state() with rcu_force_quiescent_state()

This patch merges the function rcu_force_quiescent_state() with
rcu_sched_force_quiescent_state(), using the rcu_state pointer.  Firstly,
the rcu_sched_force_quiescent_state() function is deleted from the file
kernel/rcu/tree.c. Also, the rcu_force_quiescent_state() function that was
calling force_quiescent_state with the argument rcu_preempt_state pointer
was deleted as well.  The new function that combines the old ones uses
the rcu_state pointer and is located after rcu_batches_completed_bh()
in kernel/rcu/tree.c.

Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>