According to A8.6.189 STM/STMIA/STMEA (Encoding T1), there's only tSTMIA_UPD available.
Ignore tSTMIA for the decoder emitter and add a test case for that.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128246 91177308-0d34-0410-b5e6-96231b3b80d8