* new helper atapi_cdb_len() in linux/ata.h, use it after
IDENTIFY PACKET DEVICE command completes
* add new taskfile protocol ATA_PROT_ATAPI_NODATA
* store scsi cdb in ata_queued_cmd.  This removes another dependence
on the scsi layer, and enables us to issue an internal REQUEST SENSE.
* store cdb len in ata_port
* new constant ATAPI_CDB_LEN for max cdb length
* move ATA taskfile and SCSI cdb near the top of ata_queued_cmd, for
better cacheline friendliness.