mtd: nand: increase max OOB size to 640

Some Hynix and Samsung MLC NAND have 640B OOB size. Sooner or later, we should
dynamically allocate the buffers that use these macros.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>