[X86][SSE] Pulled out repeated target shuffle decodes into helper functions. NFCI.
[X86][SSE] Pulled out repeated target shuffle decodes into helper functions. NFCI.

Pulled out the code used by PSHUFB/VPERMV/VPERMV3 shuffle mask decoding into common helper functions.

The helper functions handle masks coming from BROADCAST/BUILD_VECTOR and ConstantPool nodes respectively.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@260032 91177308-0d34-0410-b5e6-96231b3b80d8

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