We regularly have new NAND controller drivers that are making use of
fields/hooks that we want to get rid of but can't because of all the
legacy drivers that we might break if we do.

So, instead of removing those fields/hooks, let's move them to a
sub-struct which is clearly documented as deprecated.

We start with the ->IO_ADDR_{R,W] fields.
Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>