arm64: Add OCIBHYVE, a kernel for bhyve guests without a loader

[dch]

Summary

• bhyve can now boot an arm64 kernel.bin directly as its boot ROM
• with no loader to load modules, the kernel needs its drivers built in
• OCIBHYVE is GENERIC without debugging options
• it adds p9fs and virtio_p9fs, for a root shared from the host
• it also adds virtio_console, virtio_random, nullfs and fdescfs
• virtio_random matters most
• without a loader nothing seeds the random device, so reads of /dev/random waited about 25 seconds
• with bhyve's virtio-rnd they no longer wait
• bhyve.8: point to OCIBHYVE
• ocibhyve, an OCI runtime that runs each container in a bhyve VM, boots its guests this way
• its agent says hello 0.19s after bhyve starts

[imp]

sys/arm64/conf/OCIBHYVE

24

For this deployment, don't you want to omit the vast majority of what we include in GENERIC? I would think that MINIMAL would be a better base to start from since GENERIC is so driver heavy and we'll never ever attach most of the drivers in it.