arch,mn10300: Convert smp_mb__*()

mn10300 fully relies on asm-generic/barrier.h and therefore its
smp_mb() is barrier(). We can use the default implementation.

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-wotyeoj99h1dpojjeest2jbk@git.kernel.org


Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-am33-list@redhat.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>