[TF-M] Design proposal: Changing secure service call in library model

Hi All,

I'm planning to change the way secure services are called in Library model.

The design proposal can be found here: https://review.trustedfirmware.org/#/c/trusted-firmware-m/+/2201/

Please note that the changes proposed by this document does not affect the PSA dev API, and does not affect IPC model.

Please share your opinion in gerrit comments

Thanks, Mate