Rework *raise_exception*() functions so that they can be called from
other helpers, passing the return address as an argument.
Use do_raise_exception() function in update_fcr31() to correctly restore
the CPU state after an FPU exception.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>