cpu: initial import of stm32f1
boards: initial import of iot-lab_M3
at86rf231: introduce variable to keep internal driver state

The at86rf231 radio transceiver provides one IRQ (TRX_END) signaling
end of transmission or reception but no way to distinguish between
these.
stm32f1: implement missing UART0 parts
iot-lab_M3: refactor at86rf231 driver
stm32f1: implement SPI register access functions
at86rf231: handle rx tx state changes correctly
stm32f1: implement new cpuid_get
stm32f1: SPI: implement speed setting properly
Merge pull request #1363 from thomaseichinger/thirdparty_boards_import

board: cpu: initial import of iot-lab_M3