configstore: add new configuration item

This change adds to configstore@1.0 HAL a new configuration item
for surfaceflinger; useTripleFramebuffer()

In the default implementation, useTripleFramebuffer() will return true
only if the build flag NUM_FRAMEBUFFER_SURFACE_BUFFERS is defined as 3.

Bug: 34723491
Test: build & run. log message "SurfaceFlinger FrameBuffer: ?"
      should be seen.

Change-Id: I7ab9f17f43d68ee7b37b5db8c24b542db4d1c216
Merged-In: Iac97e25cd69717c73a135f6b2a44538124544987
diff --git a/configstore/1.0/default/SurfaceFlingerConfigs.cpp b/configstore/1.0/default/SurfaceFlingerConfigs.cpp
index fc75182..5d62b15 100644
--- a/configstore/1.0/default/SurfaceFlingerConfigs.cpp
+++ b/configstore/1.0/default/SurfaceFlingerConfigs.cpp
@@ -19,6 +19,15 @@
     return Void();
 }
 
+Return<void> SurfaceFlingerConfigs::useTripleFramebuffer(useTripleFramebuffer_cb _hidl_cb) {
+    bool value = false;
+#ifdef USE_TRIPLE_FRAMEBUFFER
+    value = true;
+#endif
+    _hidl_cb({true, value});
+    LOG(INFO) << "SurfaceFlinger FrameBuffer: " << (value ? "triple" : "double");
+    return Void();
+}
 
 // Methods from ::android::hidl::base::V1_0::IBase follow.