sparc64: refactor the ali DMA quirk

Do the quirk first in the dma_supported routines, as we don't need
any of the other checks for it, and remove the duplicate mask checking
that is already done by the callers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: David S. Miller <davem@davemloft.net>