Add dtmSupported into 1.6 HAL for 2G network

Bug: 178328574
Test: make, VTS
Change-Id: Iba230acda8302df90e77d93701d9b0ba74196fc0

radio/1.6/types.hal

@@ -737,6 +737,14 @@ struct RegStateResult {
              */
             NrVopsInfo nrVopsInfo;
         } ngranInfo;
+
+        struct GeranRegistrationInfo {
+            /**
+             * True if the dual transfer mode is supported.
+             * Refer to 3GPP TS 44.108 section 3.4.25.3
+             */
+            bool dtmSupported;
+        } geranInfo;
     } accessTechnologySpecificInfo;
 };