- Clean up pmap_bootstrap() some, and make a slight change to how the
PROM mappings are saved.
- Give each pmap its own level 1 page table, rather than sharing a global
level 1 page table. This will eventually allow for Very Large user
address spaces.
- Keep a list of all pmaps, so that when kernel level 2 page tables are
allocated, all level 1 tables may be updated.
- Add a couple of functions for allocating and freeing page table pages.
- Add a few comments about ASN allocation.