[TF-M] Start of TF-M v1.8.0 release

Hello,

The branch release/1.8.xhttps://git.trustedfirmware.org/TF-M/trusted-firmware-m.git/log/?h=release/1.8.x has been created indicating the start of the release process and features freeze. RC1 tag will follow after a successful run of the basic tests.

Let me remind that the code is not frozen, and development can be continued on the main branch as described in TF-M Release Processhttps://tf-m-user-guide.trustedfirmware.org/releases/release_process.html#release-cadence-and-process.

Thanks, Anton