Merge the recent commits of FBGEMM and remove unnecessary CMake code.
Specifically, we
1. enable `fbgemm_autovec` since the target is now correctly handled.
2. remove option `USE_FAKELOWP` which is not used.
3. remove `CAFFE2_COMPILER_SUPPORTS_AVX512_EXTENSIONS` check.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/158210
Approved by: https://github.com/q10