first VEX ymm vector ops

   - 32x8 i32 add,sub,mul
   - add I32_Naive bench/test builder to get better i32 mul coverage
   - minor refactoring all over

Change-Id: I13cc19ff37a2da0bcff289ba51baac08f456d6c5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/222485
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
7 files changed