Legacy NAND had been scheduled for removal.  Any boards that use this
were already not building in the previous release due to an #error.

The disk on chip code in common/cmd_doc.c relies on legacy NAND,
and it has also been removed.  There is newer disk on chip code
in drivers/mtd/nand; someone with access to hardware and sufficient
time and motivation can try to get that working, but for now disk
on chip is not supported.

Signed-off-by: Scott Wood <scottwood@freescale.com>