dumpstate HAL uses "default" service name

The getService() and registerAsService() methods of interface objects
now have default parameters of "default" for the service name. HALs
will not have to use any service name unless they want to register
more than one service.

Test: builds

Bug: 33844934
Change-Id: I4415e38d0f50884e31feedddf8e4236fa69f1a31

dumpstate/1.0/default/service.cpp

@@ -29,6 +29,6 @@ using ::android::sp;
 int main (int /* argc */, char * /* argv */ []) {
     sp<IDumpstateDevice> dumpstate = new DumpstateDevice;
     configureRpcThreadpool(1, true);
-    dumpstate->registerAsService("dumpstate");
+    dumpstate->registerAsService();
     joinRpcThreadpool();
 }