Added schedule point for functions executed once in a second SPI communication takes place every 100ms triggered by the master (main). Synchronisation is done using the SPI RX complete callback which is called ~4ms after communication was started. In the previous implementation this could happen in parallel to usage of data. To solve this potential problem the execution of functions called once a second was moved from 1000ms to 980ms giving a 20ms window for execution.

Imported from Ac6/SystemWorkbench/plugins/fr.ac6.mcu.firmware_1.14.7.201711101414/resources/builtin/:
* File syscalls.c