Cleanup Gnss UART implementation: The first draft of the internal UART implementation was just a copy of the external UART handling. To avoid duplicated code and maintainance issue both UARTs (external/internal 6/1) share the same functions. To enable this a control structure has to be used as function input which defines the none shared resources like DMA control and rx/tx buffers

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