ipc/util.c, ipc_rcu_alloc: cacheline align allocation

ipc/util.c, ipc_rcu_alloc: cacheline align allocation

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.

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>