mtd-utils: support 4096+64 page sizes

mtd-utils: support 4096+64 page sizes

Add support for oobsize 64 and writesize 4096 in nanddump & nandwrite.

Artem: some more info from further e-mail exchange:

> Are there flashes with the 4096 page / 64 spare combination? Could you
> refer to one? May be any URL? I thought 4096 comes with 128.

Much to my regret I can't provide a URL because is not public. IGEP v2
board has a Onenand with two dice of 2048/64 spare combination but mtd
views 4096/64. The minimal write page is 4K (2K from first dice and 2K
from second dice).

Signed-off-by: Enric Balletbo i Serra <eballetbo@iseebcn.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>