docs: Cleaning up optee_design.md
docs: Cleaning up optee_design.md

- Removed information that isn't up-to-date (better to remove it than
  having the wrong information).
- Fixed various links etc.
- Created some tables to make things more readable.
- Formatted according to 80 character width.
- Added links in the table of contents.

Signed-off-by: Joakim Bech <741f90e2a7f4d9afbad8bd50be20560f4cf38962@linaro.org>
Reviewed-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@linaro.org>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os