esp.c: handle TC underflow for DMA SCSI requests

esp.c: handle TC underflow for DMA SCSI requests

Detect the case where the guest underflows TC by requesting a DMA transfer which
is larger than the available data. If this case is detected, immediately
complete the SCSI request and handle any remaining FIFO accesses in the STATUS
phase by raising INTR_BS once the FIFO is below the threshold.

Note that handling the premature SCSI bus phase change in the case of TC
underflow fixes booting EMILE on m68k once again.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Tested-by: Helge Deller <deller@gmx.de>
Tested-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20240112125420.514425-73-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>