Patch originally by Matt Dobson. Reworked a little by me.

Stores the mappings between cpus and nodes in an array, instead of
working them out every time. Gives about 4% off systime for kernel
compile (we use these for every page allocation), and removes one
of the two only usages of apicid->cpu mapping, which is really awkward
to keep for systems with large apic spaces, and is genererally pretty
useless anyway (later patch removes).