Add definitions for the PPC a2q core marked as having QPX available

This is the first commit of a large series which will add support for the
QPX vector instruction set to the PowerPC backend. This instruction set is
used on the IBM Blue Gene/Q supercomputers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173973 91177308-0d34-0410-b5e6-96231b3b80d8