percpu: convert spin_lock_irq to spin_lock_irqsave.

percpu: convert spin_lock_irq to spin_lock_irqsave.

From Michael Cree:
  "Bisection lead to commit b38d08f3181c ("percpu: restructure
   locking") as being the cause of lockups at initial boot on
   the kernel built for generic Alpha.

   On a suggestion by Tejun Heo that:

   So, the only thing I can think of is that it's calling
   spin_unlock_irq() while irq handling isn't set up yet.
   Can you please try the followings?

   1. Convert all spin_[un]lock_irq() to
      spin_lock_irqsave/unlock_irqrestore()."

Fixes: b38d08f3181c ("percpu: restructure locking")
Reported-and-tested-by: Michael Cree <mcree@orcon.net.nz>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Dennis Zhou <dennis@kernel.org>