[X86][AVX] Enabled SMUL_LOHI/UMUL_LOHI v8i32 vectors on AVX1 targets

Correct splitting of v8i32 vectors into v4i32 vectors to prevent scalarization

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264517 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed