Add a simple driver for vms.

Not being called yet, compiles. Waiting for comments from Barret et. al.
Please note I don't use TAILQ because I expect far higher read
than change traffic on the vm array and a simple array is a lot more
cache friendly.

If this is ok, then I'll add in the support code from the litevm project
and, voila, we have VMs maybe.

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