[X86] Rename matchBitOpReduction to matchScalarReduction. NFCI. This doesn't need to be just for bitops, but the ops do need to be fully associative. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375445 91177308-0d34-0410-b5e6-96231b3b80d8