[mips][mips64r6] Add bc[12](eq|ne)z

Summary: Depends on D3691

Reviewers: jkolek, zoran.jovanovic, vmedic

Reviewed By: vmedic

Differential Revision: http://reviews.llvm.org/D3760

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209292 91177308-0d34-0410-b5e6-96231b3b80d8