DragonFlyBSD

Import of virtio and virtio-blk drivers from Tim Bisson and FreeBSD.

• dump seems to not work (panic)
• serno support seems to not work?
• reloading the module doesn't work
• is a spinlock most appropriate for a per-target lock?

• lock-splitting -- bioq can use a different lock than per-target spinlock.

Updated; tied into the build process, enabled on i386 and x86-64 GENERIC.

-- vs;