So I just checked in a patch to use DMA to transfer message/command
during select. The code is activated by setting the variable
`ncr53c9x_selectdma' to 1, so other ports aren't screwed immediately
if all this doesn't do the right thing.

Note: in the sparc ESP/DMA code I hade to remove an NCRCMD_FLUSH that
interfered with DMA enabled selection. The flush is unnecesary at
that point since the NCR driver will do all required flushing eventually.
This applies to the alpha and sun3x DMA code as well!

I believe it's possible to get a some spurious complaints about
unfinished DMA transactions when interrupted by another target
that's reselecting. This will need some attention later.

-pk