tfm: Change SFN and FP_HARDABI dependency

TF-M only suports floating point in IPC model, not the SFN model.
Since floating point is a basic feature of the architecture and TF-M
has the limitation it makes more sense for the dependency to exist in
TF-M and and limit the TF-M model choice instead of limiting the
option to enable floating point.

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