IVGCVSW-5636 'Implement NNAPI caching functions'

* Get number of inputs and outputs from optimized network.
* Get number of cached files if backend supports caching.

Signed-off-by: Sadik Armagan <sadik.armagan@arm.com>
Change-Id: Ie02ac123bb7df9b0593a2fe46b5bb564a5994780
diff --git a/include/armnn/backends/IBackendInternal.hpp b/include/armnn/backends/IBackendInternal.hpp
index 7500e35..9253e11 100644
--- a/include/armnn/backends/IBackendInternal.hpp
+++ b/include/armnn/backends/IBackendInternal.hpp
@@ -206,6 +206,11 @@
     {
         throw armnn::Exception("GetDefaultAllocator: Function has not been implemented in backend.");
     }
+
+    /// Returns the number of files cached if backend supports caching
+    ///
+    /// \return - Returns 0 if backend does not support caching otherwise number of files cached
+    virtual unsigned int GetNumberOfCacheFiles() const { return 0; }
 };
 
 using IBackendInternalUniquePtr = std::unique_ptr<IBackendInternal>;