IVGCVSW-3014 Add GetSupportedBackends to IDeviceSpec

Signed-off-by: Narumol Prangnawarat <narumol.prangnawarat@arm.com>
Change-Id: I8d6474389376f715074bfa7a75613dbda35bcc6a
diff --git a/include/armnn/Types.hpp b/include/armnn/Types.hpp
index 438b6be..53aa437 100644
--- a/include/armnn/Types.hpp
+++ b/include/armnn/Types.hpp
@@ -118,6 +118,8 @@
 protected:
     IDeviceSpec() {}
     virtual ~IDeviceSpec() {}
+public:
+    virtual const BackendIdSet& GetSupportedBackends() const = 0;
 };
 
 /// Type of identifiers for bindable layers (inputs, outputs).