[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 new instructions (except vector 32-bit float and 128-bit float).
- CodeGen for new instructions, including new LLVM intrinsics.
- Scheduler description for the new processor.
- Detection of z14 as host processor.

Support for the new 32-bit vector float and 128-bit vector float
instructions is provided by separate patches.

llvm-svn: 308194