ARM: dts: use all remaining MTD space foor rootfs of Iomega ix2-200

The original MTD partition layout for the Iomega ix2-200 leaves most of the
available space unused. This patch changes the layout to use all remaining
MTD space after the partitions for u-boot/u-boot-env and the kernel uimage
as a "rootfs" partition.

Signed-off-by: Richard Kunze <richard.kunze@web.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>