ide: remove the PCI_DMA_BUS_IS_PHYS check

We now have ways to deal with drainage in the block layer, and libata has
been using it for ages.  We also want to get rid of PCI_DMA_BUS_IS_PHYS
now, so just reduce the PCI transfer size for ide - anyone who cares for
performance on PCI controllers should have switched to libata long ago.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>