hwcomposer 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: I6befd081add61e355bc25dd0c630ac07ea0103c4
diff --git a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
index 3e9ef24..c6e6dcb 100644
--- a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
+++ b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
@@ -131,7 +131,7 @@
     if (mIsUsingVrComposer) {
         mComposer = IComposer::getService("vr_hwcomposer");
     } else {
-        mComposer = IComposer::getService("hwcomposer");
+        mComposer = IComposer::getService(); // use default name
     }
 
     if (mComposer == nullptr) {