Initial import of MSB-IoT board

Pull request contains basic support for the MSB-IoT board used at CST group at FU Berlin. It also adds support for more GPIO pins and one more UART to the corresponding stm32f4 drivers.

It is already based on the proposed updated low-level driver interfaces and hence depends on:
* #1481
* #1484
You need to change this to:
```c
#if UART_0_EN
__attribute__((naked)) void UART_2_ISR(void)
{
    ISR_ENTER();
    irq_handler(UART_2, UART_2_DEV);
    ISR_EXIT();
}
#endif
```

I must have forgot to put guards around these functions...