[region] Add TosaSerializationRegion to serialization_lib

- Rationale: add this fix to support constants access between multiple
blocks by another layer of abstraction called Region
- Changes:
  - flatbuffers schema update, regenerate header files
  - add TosaSerializationRegion for the handler
  - other relevant fixes

Signed-off-by: Jerry Ge <jerry.ge@arm.com>
Change-Id: I4bb72503abfd629ae017d2f905184efbab244aa8