[PowerPC] avoid verification failure due to PowerPC VSX Swap Removal pass

[PowerPC] avoid verification failure due to PowerPC VSX Swap Removal pass

This patch fixes a failure in lnt tests with -verify-machineinstrs option.
When VSX Swap Removal pass swaps two register operands, it did not maintain kill flags associated with operands. This patch swaps flags as well as register number to avoid inconsistent kill flags information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@334579 91177308-0d34-0410-b5e6-96231b3b80d8