Because note_new_gpnum() now also checks for the ends of old grace periods,
this commit changes its name to note_gp_changes(). Later commits will merge
rcu_process_gp_end() into note_gp_changes().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>