nand: davinci: add support for driver model

Extend the davinci NAND driver to support the driver model. For now this
doesn't add any device-tree parsing due to the fact that we can't access
the actual nand node on the device-tree - it's a subnode of the aemif
device and we don't have an aemif driver on davinci at the moment.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>