For old CPUs, map the 64 first MB of RAM as it used to be. Some ports
(XScale mainly) expects the memory located before the kernel to be mapped,
and use it to allocate the page tables, the various stacks, etc.
A better fix would probably be to rewrite the various bla_machdep.c to stop
using that RAM, but I'm not so inclined to do it, especially since I don't
have hardware for all of them.
Do not hand the VM the memory used for stacks/page tables/etc.