When ARM_NONSECURE_PREEMPTIBLE_SECURE_CALLS is enabled, if FPU is
being used (CONTROL.FPCA == 1), store all FP registers before
entering the secure function, and restore them afterwards.
This is needed if any NS thread or ISR that interrupts the secure
function uses FP registers. If they do, a secure UsageFault occurs
unless this change is applied.
This allows k_sched_lock() and k_sched_unlock() to be dropped when
ARM_NONSECURE_PREEMPTIBLE_SECURE_CALLS is enabled.
Enable ARM_NONSECURE_PREEMPTIBLE_SECURE_CALLS by default when
building TF-M.
Signed-off-by: Øyvind Rønningstad <oyvind.ronningstad@nordicsemi.no>
aed0643705