nand/mpc512x: Add MPC512x NAND support (NFC)

This patch adds NAND Flash Controller driver for MPC5121 revision 2.
All device features, except hardware ECC and power management, are
supported.

This NFC driver replaces the one orignally posted by John Rigby:

"[PATCH] Freescale NFC NAND driver"

It's a port of the Linux driver version posted by Piotr Ziecik a few
weeks ago. Using this driver has the following advantages (from my
point of view):

- Compatibility with the Linux NAND driver (e.g. ECC usage)
- Better code quality in general
- Resulting U-Boot image is a bit smaller (approx. 3k)
- Better to sync with newer Linux driver versions

The only disadvantage I can see, is that HW-ECC is not supported right
now. But this could be added later (e.g. port from Linux driver after
it's supported there). Using HW-ECC on the MCP5121 NFC has a general
problem because of the ECC usage in the spare area. This collides with
JFFS2 for example.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Piotr Ziecik <kosmo@semihalf.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: John Rigby <jcrigby@gmail.com>
Cc: Scott Wood <scottwood@freescale.com>