Optimized GetScalarNZM, add limit to how far it can recurse. Add rlwinm elimination rule

src/xenia/cpu/hir/value.h

@@ -577,6 +577,7 @@ class Value {
   void ByteSwap();
   void CountLeadingZeros(const Value* other);
   bool Compare(Opcode opcode, Value* other);
+  hir::Instr* GetDefSkipAssigns();
 
  private:
   static bool CompareInt8(Opcode opcode, Value* a, Value* b);