stm32f429i-disco: add wrapper for spi5 evice

initializing

As long as the method up_spiinitialize recognized the initialized state of the
spi device by the spi enable flag of the cr1 register, it isn't safe to disable
the spi device outside of the nuttx spi interface structure. But this has to be
done as long as the nuttx spi interface doesn't support bidirectional data
transfer for multiple devices share one spi bus. This wrapper store the
initialized state of the spi device after the first initializing and should be
used by each driver who shares the spi5 bus.

Note! Understand this as temporary workaround.

Signed-off-by: Marco Krahl <ocram.lhark@gmail.com>