VideoConfig: Limit the Stereo 3D option to the OpenGL backend.

Source/Core/VideoBackends/OGL/main.cpp

@@ -138,6 +138,7 @@ static void InitBackendInfo()
 	//g_Config.backend_info.bSupportsDualSourceBlend = true; // is gpu dependent and must be set in renderer
 	//g_Config.backend_info.bSupportsEarlyZ = true; // is gpu dependent and must be set in renderer
 	g_Config.backend_info.bSupportsOversizedViewports = true;
+	g_Config.backend_info.bSupportsStereoscopy = true;
 
 	g_Config.backend_info.Adapters.clear();