arch,alpha: Convert smp_mb__*() to the asm-generic primitives

The Alpha ll/sc primitives do not imply any sort of barrier; therefore
the smp_mb__{before,after} should be a full barrier. This is the
default from asm-generic/barrier.h and therefore just remove the
current definitions.

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-iacwfd15lq3ta2v7jut747r7@git.kernel.org


Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: linux-alpha@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>