esp.c: remove restriction on FIFO read access when DMA memory routines defined

esp.c: remove restriction on FIFO read access when DMA memory routines defined

The latest state machines can handle mixing DMA and non-DMA FIFO access for all
SCSI phases except DATA IN and DATA OUT. For DATA IN and DATA OUT phases, the
transfer is complete when TC == 0 and the updated logic will now handle TC
underflow correctly, which makes it just about impossible to manually manipulate
the FIFO during a DMA transfer.

Remove the restriction on FIFO read access when DMA memory routines are defined
which also allows the NeXTCube machine to pass its self-test.

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: <20240112125420.514425-74-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>