IVGCVSW-2697 Add Serialize/Deserialize for the Merger Layer

IVGCVSW-2697 Add Serialize/Deserialize for the Merger Layer

* Force generation of schema header in every build
* Also fixed typo in OriginsDescriptor comment (Descriptors.hpp)
* Added Serialize/Deserialize check on Addition Layer
* Added Serialize/Deserialize check on Floor Layer
* Added Serialize/Deserialize check on Minimum Layer
* Added Serialize/Deserialize check on Maximum Layer
* Added Serialize/Deserialize check on Multiplication Layer
* Added Serialize/Deserialize check on Division Layer

Change-Id: I1358ea4db7ca506d8bcec2ee64e1fbad6005e723
Signed-off-by: Jim Flynn <jim.flynn@arm.com>