esp-scsi: terminate DMA transfer when ESP data transfer completes

esp-scsi: terminate DMA transfer when ESP data transfer completes

When the ESP data transfer completes indicated by the STAT_TC flag being set,
terminate the DMA transfer by issuing a DMA IDLE command. Otherwise in the case
where the guest sends a reset followed by an ESP command, the DMA signal remains
enabled and so the next SeaBIOS DMA transfer begins immediately when the next
ESP command is received rather than waiting until the data is ready and the DMA
command is issued.

With this fix it is possible to boot a Windows XP ISO to the installer and
complete a full installation within QEMU directly using SeaBIOS.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Message-ID: <20240101121942.383191-1-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>