Change DevicesBitfield type to struct

Change-Id: I7a005b07737cdd21efc174a2ee2be0f6b7f9068d
Signed-off-by: Jablonski, Mateusz <mateusz.jablonski@intel.com>

runtime/memory_manager/definitions/devices_bitfield.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (C) 2019 Intel Corporation
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ */
+
+#pragma once
+namespace OCLRT {
+struct DevicesBitfield {
+};
+} // namespace OCLRT