[op-tee] Preparing for OP-TEE 3.9.0

[BCC all OP-TEE maintainers]

Hi OP-TEE maintainers & contributors,

We're about to make another OP-TEE release, namely: 3.9.0. Target is Friday, May 22th which leaves us almost 3 weeks to finalize the release.

Please start testing your favorite platform(s) and report any issue in this pull request [1]. I will create a release candidate tag one week before the release date, at which point we will do some more testing and I will collect Tested-by tags in the same pull request.

[1] https://github.com/OP-TEE/optee_os/pull/3833

Thanks!

Regards, Jens