tests/posix_sleep: dont use periph_rtt for efm32 and kinetis
tests/posix_sleep: dont use periph_rtt for efm32 and kinetis

These CPU families have a non configurable RTT of 1Hz, not enough for
ztimer_msec to run on periph_rtt.

ant9000/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OTAkeys/RIOT,kYc0o/RIOT,authmillenon/RIOT,kYc0o/RIOT,OlegHahm/RIOT,ant9000/RIOT,ant9000/RIOT,authmillenon/RIOT,OlegHahm/RIOT,miri64/RIOT,kYc0o/RIOT,jasonatran/RIOT,OTAkeys/RIOT,jasonatran/RIOT,miri64/RIOT,OlegHahm/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,ant9000/RIOT,kaspar030/RIOT,jasonatran/RIOT,authmillenon/RIOT,authmillenon/RIOT,authmillenon/RIOT,OTAkeys/RIOT,kaspar030/RIOT,kaspar030/RIOT,kYc0o/RIOT,miri64/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT