ARM: IGEP0033: Add support to boot from NAND.

Add to the default environment the possibily to boot from NAND using
a ubi rootfs. Also the partition scheme is set as follows:

                  Start      Size
    SPL         : 0x00000000 0x00080000 (512KiB)
    U-Boot      : 0x00080000 0x00100000 (1MiB)
    U-Boot Env  : 0x00180000 0x00020000 (128KiB)
    File System : 0x001C0000 -

The ubiboot script gets the kernel and the dtb file from the boot directory
of the File System.

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Reviewed-by: Javier Martinez Canillas <javier@dowhile0.org>