sata_mv: more interrupt handling rework

Continue fixing the interrupt handling logic.

Get rid of mv_intr_pio(), by using ata_sff_host_intr() for PIO..

Add a mv_unexpected_intr() catch-all for "impossible" scenarios,
where we get an interrupt that shouldn't have happened
(never seen in testing, but just in case..).

Rearrange the logic so that we always process completed
response queue entries before looking for other events,
This avoids having to re-issue commands that had already succeeded.

As part of this, we split out some duplicated functionality
into a new function, mv_get_active_qc().

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>