[Power9] Add support for -mcpu=pwr9 in the back end

This patch corresponds to review:
http://reviews.llvm.org/D19683

Simply adds the bits for being able to specify -mcpu=pwr9 to the back end.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268950 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed