core/arm: Improve timing accuracy before service calls in JIT

We also correct the CPU JIT's implementation of Step.

src/core/core.h

@@ -50,10 +50,10 @@ public:
      * is not required to do a full dispatch with each instruction. NOTE: the number of instructions
      * requested is not guaranteed to run, as this will be interrupted preemptively if a hardware
      * update is requested (e.g. on a thread switch).
-     * @param tight_loop Number of instructions to execute.
+     * @param tight_loop If false, the CPU single-steps.
      * @return Result status, indicating whethor or not the operation succeeded.
      */
-    ResultStatus RunLoop(int tight_loop = 1000);
+    ResultStatus RunLoop(bool tight_loop = true);
 
     /**
      * Step the CPU one instruction