Standardize the NAND controller/NAND chip DT representation. Now, all new
NAND controller drivers should comply with this representation, even if
they are only supporting a single NAND chip.

Existing drivers can keep support for the old representation (where only
the NAND chip was described), but are encouraged to also support the new
one.
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: NBrian Norris <computersforpeace@gmail.com>
Acked-by: NRob Herring <robh@kernel.org>