arch,sparc: Convert smp_mb__*()

sparc32: fully relies on asm-generic/barrier.h and thus can use its
	 implementation.

sparc64: is strongly ordered and its atomic ops imply a full barrier,
	 implement the new primitives using barrier().

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David S. Miller <davem@davemloft.net>
Link: http://lkml.kernel.org/n/tip-2cla9ubpd8chrntnm7e4zdt4@git.kernel.org


Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org
Cc: sparclinux@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>