soundtrigger: Use "default" instance name for HAL service

"default" implies using "primary" legacy device module.
This doesn't change anything for binderized mode, because
the server was only registering itself as "sound_trigger.primary",
so it was the only possibility anyways.

Usage of "stub" (debugging) module is still possible
if audioflinger and corresponding services are built with
USE_LEGACY_LOCAL_AUDIO_HAL=true (added makefile check to ensure
that).

Test: "Ok Google" from screen off state on sailfish
Bug: 36570720
Change-Id: I88f1ebd4c1efd0f91e37458746c336a4beef33ae
diff --git a/audio/2.0/default/service.cpp b/audio/2.0/default/service.cpp
index f3a858a..7f28d7d 100644
--- a/audio/2.0/default/service.cpp
+++ b/audio/2.0/default/service.cpp
@@ -50,7 +50,7 @@
     status = registerPassthroughServiceImplementation<IEffectsFactory>();
     LOG_ALWAYS_FATAL_IF(status != OK, "Error while registering audio effects service: %d", status);
     // Soundtrigger and FM radio might be not present.
-    status = registerPassthroughServiceImplementation<ISoundTriggerHw>("sound_trigger.primary");
+    status = registerPassthroughServiceImplementation<ISoundTriggerHw>();
     ALOGE_IF(status != OK, "Error while registering soundtrigger service: %d", status);
     if (useBroadcastRadioFutureFeatures) {
         status = registerPassthroughServiceImplementation<