rcu: Add diagnostics to grace-period cleanup

At grace-period initialization time, RCU checks that all quiescent
states were really reported for the previous grace period.  Now that
grace-period cleanup has been split out of grace-period initialization,
this commit also performs those checks at grace-period cleanup time.

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