[X86] Adding avx512_vpopcntdq feature set and its intrinsics

[X86] Adding avx512_vpopcntdq feature set and its intrinsics

AVX512_VPOPCNTDQ is a new feature set that was published by Intel.
The patch represents the Clang side of the addition of six intrinsics for two new machine instructions (vpopcntd and vpopcntq).
It also includes the addition of the new feature set.

Differential Revision: https://reviews.llvm.org/D33170

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303857 91177308-0d34-0410-b5e6-96231b3b80d8