Placeholder for vm support

vm.c gets lots of errors, but I think they're going to prove
to be pretty simple.

One thing we can do cleanly in akaros, since we know we want
a vm and we know we're only going to go with one, is put the
per-cpu stuff in the actual akaros per-cpu structs. That gets
rid of some fiddling around.

We should figure out if msr-index.h just should go in x86.h.
Personally, I vote yes; I don't like lots of little includes and
cpp is fast enough for it not to matter.

Signed-off-by: Ronald G. Minnich <rminnich@google.com>