ahci: move PIO Setup FIS before transfer, fix it for ATAPI commands

The PIO Setup FIS is written in the PIO:Entry state, which comes before
the ATA and ATAPI data transfer states.  As a result, the PIO Setup FIS
interrupt is now raised before DMA ends for ATAPI commands, and tests have
to be adjusted.

This is also hinted by the description of the command header in the AHCI
specification, where the "A" bit is described as

    When ‘1’, indicates that a PIO setup FIS shall be sent by the device
    indicating a transfer for the ATAPI command.

and also by the description of the ACMD (ATAPI command region):

    The ATAPI command must be either 12 or 16 bytes in length. The length
    transmitted by the HBA is determined by the PIO setup FIS that is sent
    by the device requesting the ATAPI command.

QEMU, which conflates the "generator" and the "receiver" of the FIS into
one device, always uses ATAPI_PACKET_SIZE, aka 12, for the length.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180606190955.20845-3-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>