Handle ARMv6KZ naming

Summary:
* ARMv6KZ is the "canonical" name, given in the ARMARM
* ARMv6Z is an "official abbreviation" for it, mentioned in the ARMARM
* ARMv6ZK is a popular misspelling, which we should support as an alias.

The patch corrects the handling of the names.

Functional changes:
* ARMv6Z no longer treated as an architecture in its own right
* ARMv6ZK renamed to ARMv6KZ, accepting ARMv6ZK as an alias
* arm1176jz-s and arm1176jzf-s recognized as ARMv6ZK, instead of ARMv6K
* default ARMv6K CPU changed to arm1176j-s

Reviewers: rengolin, logan, compnerd

Subscribers: aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D14568

llvm-svn: 253206