drivers/stmpe811: return touch_dev position relative to top left corner
drivers/stmpe811: return touch_dev position relative to top left corner

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