libata: Support chips with 64K PRD quirk

Add ata_dumb_qc_prep and supporting logic so that a driver can just
specify it needs to be helped in this area. 64K entries are split
as with drivers/ide.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 4ddf00c..cfde22d 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2620,7 +2620,7 @@
 			ata_dev_printk(dev, KERN_WARNING,
 				       "invalid multi_count %u ignored\n",
 				       multi_count);
-	}	
+	}
 
 	/* READ/WRITE LONG use a non-standard sect_size */
 	qc->sect_size = ATA_SECT_SIZE;