Update to OP-TEE 3.20.0

[DemesneGH]

After OP-TEE 3.20.0, OP-TEE updated the GP support from 1.1 to 1.3.1 (https://github.com/OP-TEE/optee_os/pull/5688), which made some of the libutee APIs not compatible with the current Rust wrappers. So in ci.yml I've pinned the OP-TEE repo to 3.20.0.

Notes: todo list before updating to OP-TEE 3.21.0:

• re-generate Rust wrappers for libutee in optee-utee/optee-utee-sys/src/: tee_api.rs, utee_syscalls.rs, etc.
• update the corresponding function calls in optee-utee/src.
• ci: resume the OP-TEE repo to the latest version.

[henrysun007]

Two many test files are modified. Putting the version number in one file as a macro and referencing it in other files may reduce the modified files when there is a new version number.

[DemesneGH]

@henrysun007 Thanks for your comment. Since this PR was merged, I'll update those test scripts before the next version (OP-TEE 3.21.0).