[x64] Add GFNI and AVX512VBMI optimization for VECTOR_SHL(int8)

[Wunkolo]

Uses {v}gf2p8mulb as a general int8-multiplication instruction to simulate bit-shifts.

Verified the implementation with instr__gen_vslb from #1348. Can be grabbed with:

git checkout origin/gen_tests -- src\xenia\cpu\ppc\testing\*vslb.s

[antoniodesousa]

You probably have better chance of having this merged in the Canary repo:
https://github.com/xenia-canary/xenia-canary

[Wunkolo]

Ah I'd rather contribute here at xenia's core implementation and let it find its way downstream into canary.