IVGCVSW-2709 Serialize / de-serialize the Splitter layer

IVGCVSW-2709 Serialize / de-serialize the Splitter layer

* fixed typo in Ref Merger Workload comment
* fixed typo in ViewsDescriptor comment
* made the origins descriptor accessable in the ViewsDescriptor
  (needed for serialization)
* based the unit test on the use of the splitter in the CaffeParser

Change-Id: I3e716839adb4eee5a695633377b49e7e18ec2aa9
Signed-off-by: Ferran Balaguer <ferran.balaguer@arm.com>
Signed-off-by: Francis Murtagh <francis.murtagh@arm.com>
Signed-off-by: Jim Flynn <jim.flynn@arm.com>