Add support for CLVK

This patch enables CLVK through the graph API and inside the
CLScheduler. By default the Native platform is selected.
Selecting CLVK can be done via --target=clvk.

Resolves COMPMID-4205 and COMPMID-4206

Change-Id: Ic60744980c6b8a60e776627ea677ed46be88f656
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/5475
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
diff --git a/arm_compute/runtime/CL/CLTypes.h b/arm_compute/runtime/CL/CLTypes.h
index ab973f9..cf0486c 100644
--- a/arm_compute/runtime/CL/CLTypes.h
+++ b/arm_compute/runtime/CL/CLTypes.h
@@ -58,5 +58,12 @@
     bool         is_rhs_constant{ false };       /**< True if the content of the rhs matrix is constant */
     DataType     data_type{ DataType::UNKNOWN }; /**< Data type */
 };
+
+/** List the possible OpenCL backends */
+enum class CLBackendType
+{
+    Native, /**< OpenCL native backend */
+    Clvk,   /**< CLVK backend */
+};
 } // namespace arm_compute
 #endif /* ARM_COMPUTE_RUNTIME_CLTYPES_H */