Move the generic variable definitions from the ASM at the top of

Move the generic variable definitions from the ASM at the top of
locore.S to be in C in cpu.c, machdep.c, pmap.c, or bus_space.c for
better typing/debug info.  Delete REALBASEMEM, REALEXTMEM, and
biosextmem as unused/ignored.

ok mpi@ krw@ mlarkin@