FPU configuration in TF-M is currently done inconsistently at the platform level.

The registers used for configuring the FPU are defined by the Arm Architecture, so FPU config should be unified and done correctly at the architectural level.

On Armv8-M this includes configuration to ensure that information is not leaked in FPU registers to NS when S is using the FPU.

The default will still be to disable FPU in S.