IVGCVSW-4210 Create a public API for the common backend files

 * Create a public API for the common backend files
 * Move OutputHandler to armnn internal
 * Remove unused headers

Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>
Signed-off-by: Narumol Prangnawarat <narumol.prangnawarat@arm.com>
Change-Id: I3e86d908b021e3561befa9d45158d87d2cbb18c0
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 369ffcf..3f2099e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -394,6 +394,8 @@
     src/armnn/Observable.hpp
     src/armnn/Optimizer.cpp
     src/armnn/Optimizer.hpp
+    src/armnn/OutputHandler.cpp
+    src/armnn/OutputHandler.hpp
     src/armnn/OverrideInputRangeVisitor.cpp
     src/armnn/OverrideInputRangeVisitor.hpp
     src/armnn/Profiling.cpp