ARM: dts: Karo TX25: use hardware ecc

We should use hardware ecc on i.MX. While at it, add the optional
nand-bus-width property.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>