Move AESNI generation to Skylake and Goldmont

The instruction set first appeared with Westmere, but not all processors
in that and the next few generations have the instructions. According to
Wikipedia[1], the first generation in which all SKUs have AES
instructions are Skylake and Goldmont. I can't find any Skylake,
Kabylake, Kabylake-R or Cannon Lake currently listed at
https://ark.intel.com that says "Intel® AES New Instructions" "No".

This matches GCC commit
https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01940.html

[1] https://en.wikipedia.org/wiki/AES_instruction_set

Patch By: thiagomacieira
Differential Revision: https://reviews.llvm.org/D51510

llvm-svn: 341862