NVMM sync up from DragonFlyBSD

[Emile 'iMil' Heitor <imil%home.imil.net@localhost>]

I've synced up our NVMM code (kmod, lib and tool) with its current
state in DragonFlyBSD; if you're using NVMM on NetBSD as your
hypervisor you might want to give it a try 
https://github.com/NetBSD/src/compare/trunk...NetBSDfr:NetBSD-src:nvmm

I've also added a vmware compatible CPU frequency cpuid leaf which can
be used to get CPU frequency from the host instead of doing spending
100ms in DELAY(). Qemu knows hot to expose it via the -cpu host,+invtsc
flag.

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Emile `iMil' Heitor <imil@{home.imil.net,NetBSD.org}> | https://imil.net