sata_promise: handle ATAPI_NODATA ourselves

This patch extends sata_promise to handle ATAPI_NODATA
commands internally. However, commands destined to
ATA_DFLAG_CDB_INTR devices are excluded from this and
continue to be returned to libata.

Concrete changes:
- pdc_atapi_dma_pkt() is renamed to pdc_atapi_pkt(), and is
  extended to set up correct headers for NODATA packets
- pdc_qc_prep() calls pdc_atapi_pkt() for ATAPI_NODATA
- pdc_host_intr() handles ATAPI_NODATA
- pdc_qc_issue_prot() sends ATAPI_NODATA packets via the
  chip's packet mechanism, except for CDB_INTR devices

Tested on first- and second-generation chips, SATAPI and PATAPI,
with no observable regressions.

Signed-off-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Jeff Garzik <jeff@garzik.org>