pata_ali: disable ATAPI DMA

ATAPI DMA just doesn't work reliably on pata_ali.  The IDE driver can
do it but for some mysterious reason, pata_ali can't.  This patch
disables it by default and makes the driver whine during
initialization.  "pata_ali.atapi_dma" parameter is added so that user
can bypass the workaround.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>