mx28evk: Use 512k for fdt partition to align it

Using 512k for fdt partition allow it to be aligned with the other
small partitions and 512k erase block size.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
mx28evk: Add 'nandboot' environment command

This reads the kernel, ftd and boot into ubifs filesystem. While on
that, the SD firmware filename definition has been moved next to the
other SD related commands.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
mx28evk: Extend environment to easy write of NAND system

This adds following new targets:

 - update_nand_kernel
 - update_nand_fdt
 - update_nand_filesystem

and to avoid confusion, the 'update_nand_full' has been renamed to
'update_nand_firmware_full'.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
mx6sabresd: Use mmcblk0 for CONFIG_MMCROOT

Using mmcblk0 for CONFIG_MMCROOT, so that the rootfs can be found on both
FSL 3.0.35 as well as in mainline kernel.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>