util: Make x86-add-xcr0 work for testlib checkpoints

Change-Id: I7b93d7afc7710bd43412a77a204ce8838d0bfb4e

util/cpt_upgraders/x86-add-xcr0.py

@@ -44,3 +44,11 @@ def upgrader(cpt):
                 # Add the default value of XCR0 (1) if missing
                 regVals = f"{regVals} 1"
                 cpt.set(sec, "regVal", regVals)
+        elif re.search(rf"board\.processor\.cores.*isa$", sec):
+            # ISA name doesn't appear to be anywhere in the checkpoint.
+            # Assume it is X86.
+            regVals = cpt.get(sec, "regVal")
+
+            # Add the default value of XCR0 (1) if missing
+            regVals = f"{regVals} 1"
+            cpt.set(sec, "regVal", regVals)