sparc: reuse asm-generic/barrier.h

On sparc 64 bit dma_rmb, dma_wmb, smp_store_mb, smp_mb, smp_rmb,
smp_wmb, read_barrier_depends and smp_read_barrier_depends match the
asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

nop uses __asm__ __volatile but is otherwise identical to
the generic version, drop that as well.

This is in preparation to refactoring this code area.

Note: nop() was in processor.h and not in barrier.h as on other
architectures. Nothing seems to depend on it being there though.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>