[ONOS-4753] Identity/identityref implementation and UT

Change-Id: I40148fa228465555be3bdf410cc294ffc0f34c18
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/ResolvableType.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/ResolvableType.java
index 80ee4a0..ad00cae 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/ResolvableType.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/ResolvableType.java
@@ -39,5 +39,15 @@
     /**
      * Identifies the leafref.
      */
-    YANG_LEAFREF
+    YANG_LEAFREF,
+
+    /**
+     * Identifies the base.
+     */
+    YANG_BASE,
+
+    /**
+     * Identifies the identityref.
+     */
+    YANG_IDENTITYREF
 }