[X86] Move 128-bit shuffle mask widening check into lowerV2X128VectorShuffle to reduce code duplication. Use the now available widened mask to simplify some code inside lowerV2X128VectorShuffle.
[X86] Move 128-bit shuffle mask widening check into lowerV2X128VectorShuffle to reduce code duplication. Use the now available widened mask to simplify some code inside lowerV2X128VectorShuffle.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@290872 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm