[X86][SSE] Move setTargetShuffleZeroElements closer to getTargetShuffleMask. NFCI.
[X86][SSE] Move setTargetShuffleZeroElements closer to getTargetShuffleMask. NFCI.

Keep target shuffle mask helper functions closer together.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@259034 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit e9abc8ca75bd65d7c25fc0e18a01daa5eaaf4d4b)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm