- Add the appropriate cpuid checks to detect AVX2 in base/cpu
- Add FLAG_enable_avx2

AVX2 depends on AVX support, + a cpuid check with eax=7. This is similar
to chromium/src/base/cpu.cc check for AVX2.

Bug: v8:11258
Change-Id: Ia547c22e51b03fec823f5e48ebb055139632c942
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2589050Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71821}