[X86][SSE] Replace (V)CVTDQ2PD(Y) and (V)CVTPS2PD(Y) lossless conversion intrinsics with generic IR

Followup to D20528 clang patch, this removes the (V)CVTDQ2PD(Y) and (V)CVTPS2PD(Y) llvm intrinsics and auto-upgrades to sitofp/fpext instead.

Differential Revision: http://reviews.llvm.org/D20568

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270678 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed