arch,blackfin: Convert smp_mb__*()

Blackfin's atomic primitives do not imply a full barrier as whitnessed
from its SMP smp_mb__{before,after}_clear_bit() implementations.

However since !SMP smp_mb() reduces to barrier() remove everything and
rely on the asm-generic/barrier.h implentation.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-1widdkdsb3c1titq8jez6g3g@git.kernel.org


Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Steven Miao <realmz6@gmail.com>
Cc: adi-buildroot-devel@lists.sourceforge.net
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>