[SystemZ] Add support for IBM z14 processor (1/3)

This patch series adds support for the IBM z14 processor.  This part includes:
- Basic support for the new processor and its features.
- Support for low-level builtins mapped to new LLVM intrinsics.

Support for the -fzvector extension to vector float and the new
high-level vector intrinsics is provided by separate patches.

llvm-svn: 308197