[X86] Add versions of the avx512 gather intrinsics that take the mask as a...

[X86] Add versions of the avx512 gather intrinsics that take the mask as a vXi1 vector instead of a scalar

In keeping with our general direction of having the vXi1 type present in IR, this patch converts the mask argument for avx512 gather to vXi1. This can avoid k-register to GPR to k-register transitions late in codegen.

I left the existing intrinsics behind because they have many out of tree users such as ISPC. They generate their own code and don't go through the autoupgrade path which only works for bitcode and ll parsing. Ideally we will get them to migrate to target independent intrinsics, but it might be easier for them to migrate to these new intrinsics.

I'll work on scatter and gatherpf/scatterpf next.

Differential Revision: https://reviews.llvm.org/D56527

llvm-svn: 351234