I've sent this to some of you ia64 folks before, but this has changed
slightly.  I'd like to send this to Andrew Morton for inclusion in -mm
in the next couple of days if everything goes OK.  Bob Picco noticed
that it didn't work because of an oversight of mine with how vmem_map
works, but I think that's fixed now.

In any case, this simplifies how all architectures set up the global
mem_map variable, and will help simplify interactions with the memory
hotplug code as well.

However, ia64 has perhaps the most complex mem_map[ initialization, and
a diverse set of configurations.  I'd much prefer to fix any corner
cases now, than try to fix it up after it's in -mm.  I'd appreciate all
of the ia64 testing I can get, especially when CONFIG_NUMA is on.

-- Dave