[X86][SSE] Relax 0/-1 vector element insertion to work for any vector with >=16bit elements

Shuffle lowering/combining now does a good job for 256/512-bit vectors - we don't need to prevent this

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305801 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed