cpu/stm32: add sampling time to F4/F7 ADC driver
cpu/stm32: add sampling time to F4/F7 ADC driver

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