rcu: Eliminate quiescent-state and grace-period-nonstart use of rsp

Now that there is only one rcu_state structure, there is less point in
maintaining a pointer to it.  This commit therefore replaces rsp with
&rcu_state in rcu_report_qs_rnp(), force_quiescent_state(), and
rcu_check_gp_start_stall().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>