LEON only needs snooping when DMA accesses are not seen on the processor
bus.  Given that coherent allocations are mapped uncached this can't
happen for those allocations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: David S. Miller <davem@davemloft.net>