[gbinder] Add model file for Coverity. JB#61912

Eliminate false positive. Help Coverity see there is no resource leak
(CID 444479).

misc/coverity_model.c

@@ -0,0 +1,8 @@
+typedef struct gbinder_remote_request GBinderRemoteRequest;
+
+void
+gbinder_remote_request_unref(
+    GBinderRemoteRequest* req)
+{
+    __coverity_free__(req);
+}