Initial memory is physical; the mmu converts it to virtual addresses, and
then it can be added to the memory pool.  Right now there is not much
difference, but the 1:1 mapping is moving soon.

Currently the free memory pool consists of a statically allocated buffer.
Replace it with a dynamic query of the amount of memory we actually booted with.

(currently limited to 1GB since we haven't mapped anything else yet).

We currently leak a pool page, because we cannot unlink the free objects
belonging to the page from the pool's free list.

Fix by having a per-page free list (containing objects only from that page).
The pages are themselves placed on a doubly linked list.  When we identify
an empty page, we can now easily drop it since the local free list only
point within the page.

Must be large enough to hold a free_object.

This implementation stores small objects in pools of similar-sized objects,
while large objects are allocated using a first-fit algorithm.  There is also
a specialized interface for allocating aligned pages.