mtd: NAND: jz4740: Remove custom {read,write}_page handlers

Now that the mtd core supports more then 64 ecc bytes we can use it instead of
some a custom hack in the jz4740 nand driver.
This patch removes the custom {read,write}_page handlers from the jz4740 nand
driver. Thus the driver will now fallback to the default handlers from the nand
core.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>