Lack one PSA FWU file in Mbed TF-M 1.3 import

[ccli8]

In Mbed OS 6.12.0, the file tfm_firmware_update_ipc_api.c is not available in TF-M import directory:
https://github.com/ARMmbed/mbed-os/tree/mbed-os-6.12.0/platform/FEATURE_EXPERIMENTAL_API/FEATURE_PSA/TARGET_TFM/TARGET_TFM_LATEST/src

Looking into tfm_ns_import.yaml, tfm_firmware_update_ipc_api.c is actually missing.
https://github.com/ARMmbed/mbed-os-tf-m-regression-tests/blob/master/tfm_ns_import.yaml