nvidia-gpu: deferred init for NvidiaGpuDevice

Adds deferred init for NvidiaGpuDevice, so that when we bind
to this, the this pointer is valid, i.e. after construction
is completed

Change-Id: I24a53d2ab9be1a2a4431368414a154b48347d2a2
Signed-off-by: Marc Olberding <molberding@nvidia.com>
diff --git a/src/nvidia-gpu/NvidiaGpuDevice.hpp b/src/nvidia-gpu/NvidiaGpuDevice.hpp
index 2f5ee76..ac83994 100644
--- a/src/nvidia-gpu/NvidiaGpuDevice.hpp
+++ b/src/nvidia-gpu/NvidiaGpuDevice.hpp
@@ -41,6 +41,8 @@
         return path;
     }
 
+    void init();
+
   private:
     void makeSensors();