mtd: atmel_nand: add NFC status error check

Add a new function to read the NFC status. Meantime, this function will
check if there is any errors in NFC.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Tested-by: Matthieu Crapet <Matthieu.Crapet@ingenico.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>