Special cases: STFSRx and STXFSRx - they operate on predefined rd=0 or rd=1, and
expect %fsr as the parameter in assembly. They are disabled (since not used)
until an encoding, both for code generation and output, is chosen.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6619 91177308-0d34-0410-b5e6-96231b3b80d8