ARM: at91: change nand flash table

Change nand flash partition table according to www.at91.com/linux4sam

more information: http://www.at91.com/linux4sam/bin/view/Linux4SAM/GettingStarted#Linux4SAM_NandFlash_demo_Memory



Signed-off-by: Bo Shen <voice.shen@atmel.com>
[minor commit message changes]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>