mtd: nand: add OMAP2/OMAP3 NAND driver

This driver is present in the OMAP tree, now pushing it to MTD.

Original author(s):
       Jian Zhang <jzhang@ti.com>

Signed-off-by: Vimal Singh <vimalsingh@ti.com>
Cc: Jian Zhang <jzhang@ti.com>
Cc: Artem Bityutskiy <dedekind@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>