[X86] Fix PR30926 - Add patterns for (v)cvtsi2s{s,d} and (v)cvtsd2s{s,d}

[X86] Fix PR30926 - Add patterns for (v)cvtsi2s{s,d} and (v)cvtsd2s{s,d}

The code emiited by Clang's intrinsics for (v)cvtsi2ss, (v)cvtsi2sd,
(v)cvtsd2ss and (v)cvtss2sd is lowered to a code sequence that includes
redundant (v)movss/(v)movsd instructions. This patch adds patterns for
optimizing these sequences.

Differential revision: https://reviews.llvm.org/D28455

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291660 91177308-0d34-0410-b5e6-96231b3b80d8