arch,c6x: Convert smp_mb__*()

arch,c6x: Convert smp_mb__*()

c6x doesn't have a barrier.h and completely relies on
asm-generic/barrier.h. Therefore its smp_mb() is barrier() and we can
use the default versions that are smp_mb().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Mark Salter <msalter@redhat.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-kl53k3pyj0rbd80jq8ralpf3@git.kernel.org
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: linux-c6x-dev@linux-c6x.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>