This SoC uses a Cortex-M4F. QEMU only implements a M4,
which is good enough. Add a TODO note in case the M4F
is added.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Delevoryas <peter@pjd.dev>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>