add bus_dma support for the vs4000 dma translation map (sgmap).
enhance the vsbus for the lance to work with it.
remove the sgmap init code from ka46/48/49.c
This is done on a physical page size basis, instead of virtual (as the
(on vax yet non-existing) bus_* routines does). This is similar to the
way uba allocation is done.
made a whole bunch of annoying bugs disappear; mostly depending on
bad use of NBPG in non-MD code. The VAX port was the only port that
used this historical "feature".
The CL* macros should probably go away totally, there is no reason
at all to keep them.
