[PowerPC] Remove unused TM member variable to unbreak build

Fix "error: private field 'TM' is not used [-Werror,-Wunused-private-field]"

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205660 91177308-0d34-0410-b5e6-96231b3b80d8