Docs: Fix broken PDF version of the User guide

- Limit FWU design document content table depth to comply with Latex
- Reduce the Design Documents content table to titles only

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: Ia9df1b2a896f7a662bdd84e671fc091a227e25e6
3 files changed