This restructures setup_arch() for i386 to make it easier to include the
i386 numa changes (for CONFIG_DISCONTIGMEM) I've been working on.  It
also makes setup_arch() easier to read.  A version of this patch is the
in 2.4 aa tree.

This does not depend on the other patches I'm submitting today, but my
discontigmem patch does depend on this one.

I've tested this patch on the following configurations: UP, SMP, SMP
PAE, multiquad, multiquad PAE.