cpu/stm32f1/include: add cpu defines for FW slots
cpu/stm32f1/include: add cpu defines for FW slots

jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update,jbeyerstedt/RIOT-OTA-update