Up until now the bottom part of ram has been identity mapped, left over
from initial bootstrapping. Set up two top level page tables: one with the
the identity map and one without. Once the kernel starts switch to the second
but keep the former around for bootstrapping secondary cpus.
Start adding support for user address spaces, currently mostly untested.
Still have to solve the problem of keeping the kernel parts of the page tables
in sync. Will probably preallocate all of the ones needed.
The virt machine is a generic target, much like the arm virt machine.
Intended to be simple to use and a good target to run large systems like
linux on. At the moment simply support booting and simple uart and timer
support.
