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/backendsCommon/test/CompatibilityTests.cpp b/src/backends/backendsCommon/test/CompatibilityTests.cpp
index 915a015..0f889f4 100644
--- a/src/backends/backendsCommon/test/CompatibilityTests.cpp
+++ b/src/backends/backendsCommon/test/CompatibilityTests.cpp
@@ -125,6 +125,8 @@
 {
     auto refBackend  = std::make_unique<RefBackend>();
     BOOST_CHECK(refBackend->HasCapability(armnn::BackendCapability::NonConstWeights));
+
+    BOOST_CHECK(!refBackend->HasCapability(armnn::BackendCapability::AsyncExecution));
 }
 
 #endif