NAND: Allow NAND and OneNAND to coexist

This removes in nand.h code that is verbatim duplicated from bbm.h,
including directly bbm.h in nand.h. The previous state of affairs
prevented compiling code for a board hosting both NAND and OneNAND chips.

Reported-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alessandro Rubini <rubini@unipv.it>
Signed-off-by: Scott Wood <scottwood@freescale.com>