TF-M: does not allow PSA Connect to proceed with IRQs locked

[ioannisg]

Describe the bug
If PSA Calls (psa_connect, psa_call, etc.) are invoked with interrupts locked in Mainline Cortex-M (that is setting BASEPRI register to a non-zero value), the PSA calls are not successful.

In particular, psa_connect calls are returning a zero (invalid) handle.

Also: the problem occurs If BASEPRI is set to a value less or equal to 32. For BASEPRI values larger than 32 the psa calls are running successfully.

This should not be a HW (core) problem, as TF-M boosts Secure priorities with AIRCR.PRIS setting at boot.

Impact
PSA calls can not execute with locked non-secure priorities.
This prevents us from calling directly sys_reboot() in non-secure builds, because this function does interrupt locking before calling reset. It might be that TF-M does not allow IRQ locking in PSA calls (unlikely, since this concerns non-secure world), but in that case this should be documented explicitly.

This is likely a TF-M bug, but since it is a problem with the integration with Zephyr, this ticket is suppose to track the resolution of this issue (possibly in upstream TFM).

[ioannisg]

Note that this issue was not present in earlier versions of TF-M.

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