[TF-M] Removing legacy veneer support from TF-M library model

Hi All,

I'm planning to remove the custom veneer support for Library model from TF-M. Please see the proposed patch here: https://review.trustedfirmware.org/#/c/trusted-firmware-m/+/1597/

Ticket for the change is: https://developer.trustedfirmware.org/T439

After this change all secure services must use the automatically generated veneer functions in 'interface/include/tfm_veneers.h', as it is described in the design: https://developer.trustedfirmware.org/w/tf_m/design/uniform_secure_service_s...

This change doesn't affect the NSPM secure functions ('TZ_.*()' and 'tfm_register_client_id()' ). This change also doesn't affect IPC model at all (i.e. psa api functions).

Regards, Mate