svm: adopt "JDK-8352738: Implement JEP 520: JFR Method Timing and Tracing"

Author: zapster

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/logging/JfrLogTag.java

@@ -46,5 +46,6 @@ enum JfrLogTag {
     PERIODIC,
     SAMPLING,
     DCMD,
-    START
+    START,
+    METHODTRACE
 }