arch: arm: Allow enabling FPU hard ABI with TF-M

Allow enabling FPU with TF-M with the following limitations:
- Only IPC mode is supported by TF-M.
- Disallow FPU hard ABI when building the NS application, the TF-M build
system does not pass the flags correctly to all dependencies.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>