A kernel panic occurs on some CPUs (notably qemu-system-x86_64) when
calling rust-cpuid's get_extended_function_info. This is fixed upstream
in commit c3ebfc553cdff98d19d29777fd85c4f9182bfb66 but has yet to make
it crates.io.
The panic can by triggered by running "ls sys:" from ion and causes
redox to become unresponsive.
This minicommit introduces two newtpyes, `Physical` and `Virtual`,
respectively. These serves as a way to segregate the different forms of
addresses to avoid the issues we had in the old kernel.
Paul Sbarra