This PR converts tabs to white spaces.
The statement I used for the conversion:
```find . -name "*.[ch]" -exec zsh -c 'expand -t 4 "$0" > /tmp/e && mv /tmp/e "$0"' {} \;```
Afterwards, I had a quick overview of the converted files to prevent odd indentation.
RIOT's gettimeofday needs to be called from syscalls.c to assure that gcc actually links it.
If an RTC if available and enabled it will be used instead.
