X86: add more GATHER intrinsics in LLVM

Corrected type for index of llvm.x86.avx2.gather.d.pd.256
  from 256-bit to 128-bit.
Corrected types for src|dst|mask of llvm.x86.avx2.gather.q.ps.256
  from 256-bit to 128-bit.

Support the following intrinsics:
  llvm.x86.avx2.gather.d.q, llvm.x86.avx2.gather.q.q
  llvm.x86.avx2.gather.d.q.256, llvm.x86.avx2.gather.q.q.256
  llvm.x86.avx2.gather.d.d, llvm.x86.avx2.gather.q.d
  llvm.x86.avx2.gather.d.d.256, llvm.x86.avx2.gather.q.d.256

llvm-svn: 159402