mtd: nand: new base driver for memory mapped nand devices

The BF537-STAMP Blackfin board had a driver for working with NAND devices
that are simply memory mapped.  Since there is nothing Blackfin specific
about this, generalize the driver a bit so that everyone can leverage it.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Scott Wood <scottwood@freescale.com>