rcu: Move RCU-related source code to kernel/rcu directory

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-commit: 4102adab9189c8ea2f0cdd2f88345fd25d2790f1
[pdaly@codeaurora.org: resolve trivial merge conflicts]
Change-Id: Id7e0c62c710e8667ebb81bdee398ae0e41d9c3b9
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>