cgd's alpha implementation. Bus tags now point to a structure of
function pointers to bus space routines rather than being an index to
one of several I/O methods making it simpler and more efficient in
handling many different busses and mapping schemes.
machine-independent code for more sane access to bus resources.
Defines:
bus_{io,mem}_{map,unmap}
bus_{io,mem}_{read,write}_{1,2,4,8}
bus_io_{read,write}_multi_{1,2,4,8}
functions, and several types to go with them.
Note: The bus_io_*_8 functions are not supported.