boards/saml1x: provide custom value for XTIMER_BACKOFF to spin for lower values
boards/saml1x: provide custom value for XTIMER_BACKOFF to spin for lower values

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