ARM: davinci: nand: specify ecc strength

Starting with kernel v3.5, it is mandatory
to specify ECC strength when using hardware
ECC. Without this, kernel panics with a warning
of the sort:

Driver must set ecc.strength when using hardware ECC
------------[ cut here ]------------
kernel BUG at drivers/mtd/nand/nand_base.c:3519!

Fix this by specifying ECC strength for the boards
which were missing this.

Reported-by: Holger Freyther <holger@freyther.de>
Cc: <stable@vger.kernel.org> #v3.5+
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>