rcu: Merge rcu_dynticks structure into rcu_data structure

Now that there is only ever one rcu_data structure per CPU, there is no
need for a separate rcu_dynticks structure.  This commit therefore adds
the rcu_dynticks fields into the rcu_data structure in preparation for
removing the rcu_dynticks structure entirely.  Note that the ->dynticks
field will be handled specially because there is a field by that name
in both structures.

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