Enforce that ipc_rcu_alloc returns a cacheline aligned pointer on SMP.

Rationale:

The SysV sem code tries to move the main spinlock into a seperate
cacheline (____cacheline_aligned_in_smp).  This works only if
ipc_rcu_alloc returns cacheline aligned pointers.  vmalloc and kmalloc
return cacheline algined pointers, the implementation of ipc_rcu_alloc
breaks that.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>