IVGCVSW-6469 Add MirrorPad FrontEnd and Ref Support

 * Added PaddingMode enum to PaddingDescriptor to enable Symmetric and
   Reflect padding.
 * Added Symmetric and Reflect Ref implementation.
 * Added Serializer & Deserializer support.
 * Added unit tests.

Signed-off-by: Matthew Sloyan <matthew.sloyan@arm.com>
Change-Id: I4bed907b31742b32ccefe5e8ca39a6f1e5bd9dee
diff --git a/include/armnn/Types.hpp b/include/armnn/Types.hpp
index 4f39ebe..deaa0b3 100644
--- a/include/armnn/Types.hpp
+++ b/include/armnn/Types.hpp
@@ -166,6 +166,17 @@
     Exclude     = 1
 };
 
+///
+/// The padding mode controls whether the padding should be filled with constant values (Constant), or
+/// reflect the input, either including the border values (Symmetric) or not (Reflect).
+///
+enum class PaddingMode
+{
+    Constant  = 0,
+    Reflect   = 1,
+    Symmetric = 2
+};
+
 enum class NormalizationAlgorithmChannel
 {
     Across = 0,