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
Did you encounter an timer interrupt being called without the interrupt being enabled for channel? I thought I implemented the driver exactly in the way, that this should not happen, so we can save the second comparison at this point -> keep ISRs as short as possible...