Fix issue with disassembler decoding CBZ/CBNZ immediates as negatives when the upper bit is set.
They should always be zero-extended, not sign extended.  Added test case.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178275 91177308-0d34-0410-b5e6-96231b3b80d8