arm nomadik: allow Nand and OneNand to coexists

The evaluation kit has both Nand and OneNand, both drivers are there
and the two configurations only select a different default for the
jffs partition. This adds the OneNand driver and cleans up storage.

Signed-off-by: Alessandro Rubini <rubini@unipv.it>
Acked-by: Andrea Gallo <andrea.gallo@stericsson.com>