- Rearrange instruction emulation contexts to use a union for the

  various types and numbers of arguments rather than trying to keep a
  constant number of arguments for all the types.

- Also create a Register type within the instructions, to hold
  register type and number.

- Modify EmulateInstructionArm.cpp to use the new register and context
  types in all the instruction emulation functions.

- Add code to emulate the STM Arm instruction.

llvm-svn: 125528