AVX512: Implement instructions encoding, lowering and intrinsics

   vinserti64x4, vinserti64x2, vinserti32x8, vinserti32x4, vinsertf64x4, vinsertf64x2, vinsertf32x8, vinsertf32x4
Added tests for encoding, lowering and intrinsics.

Differential Revision: http://reviews.llvm.org/D11893

llvm-svn: 248111