The mtip32xx used an odd mix of the old PCI and the generic DMA API,
so switch it over to the generic API entirely.

Note that this also removes a weird fallback to just a 32-bit coherent
dma mask if the 64-bit dma mask doesn't work, as that can't even happen.
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>