vibrator 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; verify HAL still works

Bug: 33844934

Change-Id: I7ad730bc5b52b9bd3c63410f6f926cbc08d0b73c

services/core/jni/com_android_server_VibratorService.cpp

@@ -43,7 +43,7 @@ static void vibratorInit(JNIEnv /* env */, jobject /* clazz */)
     if (mHal != nullptr) {
         return;
     }
-    mHal = IVibrator::getService("vibrator");
+    mHal = IVibrator::getService();
 }
 
 static jboolean vibratorExists(JNIEnv* /* env */, jobject /* clazz */)