rcu: Use simple wait queues where possible in rcutree

As of commit dae6e64d2bcfd ("rcu: Introduce proper blocking to no-CBs kthreads
GP waits") the RCU subsystem started making use of wait queues.

Here we convert all additions of RCU wait queues to use simple wait queues,
since they don't need the extra overhead of the full wait queue features.

Originally this was done for RT kernels[1], since we would get things like...

  BUG: sleeping function called from invalid context at kernel/rtmutex.c:659
  in_atomic(): 1, irqs_disabled(): 1, pid: 8, name: rcu_preempt
  Pid: 8, comm: rcu_preempt Not tainted
  Call Trace:
   [<ffffffff8106c8d0>] __might_sleep+0xd0/0xf0
   [<ffffffff817d77b4>] rt_spin_lock+0x24/0x50
   [<ffffffff8106fcf6>] __wake_up+0x36/0x70
   [<ffffffff810c4542>] rcu_gp_kthread+0x4d2/0x680
   [<ffffffff8105f910>] ? __init_waitqueue_head+0x50/0x50
   [<ffffffff810c4070>] ? rcu_gp_fqs+0x80/0x80
   [<ffffffff8105eabb>] kthread+0xdb/0xe0
   [<ffffffff8106b912>] ? finish_task_switch+0x52/0x100
   [<ffffffff817e0754>] kernel_thread_helper+0x4/0x10
   [<ffffffff8105e9e0>] ? __init_kthread_worker+0x60/0x60
   [<ffffffff817e0750>] ? gs_change+0xb/0xb

...and hence simple wait queues were deployed on RT out of necessity
(as simple wait uses a raw lock), but mainline might as well take
advantage of the more streamline support as well.

[1] This is a carry forward of work from v3.10-rt; the original conversion
was by Thomas on an earlier -rt version, and Sebastian extended it to
additional post-3.10 added RCU waiters; here I've added a commit log and
unified the RCU changes into one, and uprev'd it to match mainline RCU.

Signed-off-by: Daniel Wagner <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: Boqun Feng <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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