kernel: allow rootfs splitters to work without CONFIG_MTD_ROOTFS_SPLIT

We want to remove that old (built-in) splitter at some point.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@42804 3c298f89-4303-0410-b956-a3cf2f4a3e73