arch,avr32: Convert smp_mb__*()

arch,avr32: Convert smp_mb__*()

AVR32's mb() implementation is a compiler barrier(), therefore it all
doesn't matter, fully rely on whatever asm-generic/barrier.h
generates.

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-8gow97a7mapmnec0pvf729pj@git.kernel.org
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>