omap3: nand: ecc layout select from board file

This patch makes it possible to select sw or hw (different layout options)
ecc scheme supported by omap nand driver.

Signed-off-by: Vimal Singh <vimalsingh@ti.com>
Signed-off-by: Sukumar Ghorai <s-ghorai@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>