bootctrl 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: Idadbd59b3194a6b54e91a4beb9e295e1d00bc237

boot/1.0/vts/functional/boot_hidl_hal_test.cpp

@@ -35,7 +35,7 @@ using ::android::sp;
 class BootHidlTest : public ::testing::Test {
  public:
   virtual void SetUp() override {
-    boot = IBootControl::getService("bootctrl");
+    boot = IBootControl::getService();
     ASSERT_NE(boot, nullptr);
   }