spinlock: Add missing __raw_spin_lock_flags() stub for UP

This was only defined with CONFIG_DEBUG_SPINLOCK set, but some
obscure arch/powerpc code wants it always.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>