IVGCVSW-5783 'Add AsyncExecution Capability'

* Added AsyncExecution to the BackendCapability enum class.
* Logged a warning if backends do not support AsyncExecution capability if AsyncNetwork is created.

Signed-off-by: Sadik Armagan <sadik.armagan@arm.com>
Change-Id: I49f8467297f4b6b8e414cb6a3638a7d3f1bb886a
diff --git a/include/armnn/Types.hpp b/include/armnn/Types.hpp
index 576e67e..07d38a3 100644
--- a/include/armnn/Types.hpp
+++ b/include/armnn/Types.hpp
@@ -203,6 +203,9 @@
     /// On the other hand, non-const weights can be accessed through inputs.
     NonConstWeights,
 
+    /// Asynchronous Execution.
+    AsyncExecution,
+
     // add new enum values here
 };