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/src/backends/reference/RefBackend.hpp b/src/backends/reference/RefBackend.hpp
index c92936c..3143173 100644
--- a/src/backends/reference/RefBackend.hpp
+++ b/src/backends/reference/RefBackend.hpp
@@ -9,7 +9,7 @@
 namespace armnn
 {
 
-const std::set<armnn::BackendCapability> backendCapabilities {
+const std::set<armnn::BackendCapability> cpuRefCapabilities {
     armnn::BackendCapability::NonConstWeights,
 };