powerpc/BSC9131RDB: Enable creation of dynamic partitions for NAND

* fdt_fixup_mtdparts is called from ft_board_setup
 * Run "mtdparts default" to create NAND partition on uboot
 * Use mtdparts to create partitions dynamically rather
    than using static partitions in device tree

Signed-off-by: Ashish Kumar <Ashish.Kumar@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>