rcu: Eliminate array-index-based RCU primitives

Now that rcu_access_index() and rcu_dereference_index_check() are no
longer used, the commit removes them from the RCU API.  This means that
RCU's data dependencies now involve only pointers, give or take the
occasional cast to and then back from an integer type to do pointer
arithmetic.  This in turn eliminates the need for a number of operations
on values carrying RCU data dependencies.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: linux-edac@vger.kernel.org
Cc: Tony Luck <tony.luck@intel.com>
Acked-by: Borislav Petkov <bp@suse.de>