[X86][SSE] Generalize lowerVectorShuffleAsBlendOfPSHUFBs to work with any vXi8 type.
[X86][SSE] Generalize lowerVectorShuffleAsBlendOfPSHUFBs to work with any vXi8 type.

We still only use this for v16i8, but this cleans up the code to support v32i8/v64i8 sometime in the future.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@339679 91177308-0d34-0410-b5e6-96231b3b80d8

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