PPCInstrInfo.cpp has ended up containing several small MI-level passes, and
this is making the file harder to read than necessary. Split out
PPCVSXCopy into its own source file. NFC.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227771 91177308-0d34-0410-b5e6-96231b3b80d8