nand_spl_simple: store ecc data on the stack

Currently nand_spl_simple puts it's temp data at 0x10000 offset in SDRAM
which is likely to contain already loaded data.
The patch saves the oob data and the ecc on the stack replacing
the fixed address in RAM.

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Ilya Yanok <yanok@emcraft.com>
CC: Scott Wood <scottwood@freescale.com>
CC: Tom Rini <tom.rini@gmail.com>
CC: Simon Schwarz <simonschwarzcor@googlemail.com>
CC: Wolfgang Denk <wd@denx.de>
Signed-off-by: Scott Wood <scottwood@freescale.com>