cpu/cortexm_common: add flash_writable section to linker script
cpu/cortexm_common: add flash_writable section to linker script

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