mtd: Add new SmartMedia/xD FTL

This implements new readwrite SmartMedia/xd FTL.

mtd driver must have support proper ECC and badblock verification
based on oob parts for 512 bytes nand.

Also mtd driver must define read_oob and write_oob, which are used
to read and write both data and oob together.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>