x86: Support Intel AVX VNNI

[Jan Beulich]

On 19.10.2020 21:52, H.J. Lu wrote:
> I probably lost the track.   Let me rephrase it again.  The {vex}
> prefix for AVX VNNI is mandatory.

And let me re-ask: Why? You've made your point for the gas side
(which I don't agree with, but that's a different aspect). I'm
still not understanding your reasoning on the disassembler side.
This is why I did point out that for e.g. vaddps the different
possible encodings can't be told apart either.

Jan