Seperate rootfs_data partition

Hey all,

due to having a bootloader that writes data in the middle of the flash, I can only use the area's before/after the flash. The area before the flash is plenty for just an openwrt image; but that leaves me with about 1MiB of rootfs_data space. After the data, I have about 8MiB left. Is it possible to define the rootfs_data partition in the devicetree? Do I need to tell the buildsystem to take into account as well?