Fixed a careless mistake.

rdar://13273675.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175939 91177308-0d34-0410-b5e6-96231b3b80d8
ARM: Convenience aliases for 'srs*' instructions.

Handle an implied 'sp' operand.

rdar://11466783

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175940 91177308-0d34-0410-b5e6-96231b3b80d8