arch,cpu: Move getExecutingAsid to the ISA class.

This function was switched based on the ISA, and returned 0 on
everything except SPARC and ARM. It was used only when tracing
instruction execution with --debug-flags=Exec.

Change-Id: I70c274cb76fb229d0e2bc606ba41f458ed18ab81
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39322
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>

src/cpu/exetrace.cc

@@ -66,8 +66,10 @@ Trace::ExeTracerRecord::traceInst(const StaticInstPtr &inst, bool ran)
         if (!in_user_mode && !Debug::ExecKernel) return;
     }
 
-    if (Debug::ExecAsid)
-        outs << "A" << std::dec << TheISA::getExecutingAsid(thread) << " ";
+    if (Debug::ExecAsid) {
+        outs << "A" << std::dec <<
+            thread->getIsaPtr()->getExecutingAsid() << " ";
+    }
 
     if (Debug::ExecThread)
         outs << "T" << thread->threadId() << " : ";