dt-bindings: mtd: ingenic: Mark partitions in the controller node as deprecated

Defining partitions as subnodes of the controller has been deprecated
long time ago, but unlike having partitions within the controller node,
having an enveloppe named "partitions" (which is not itself within a
chip subnode) is not that common, so keep this deprecated definition in
this file.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20221114090315.848208-7-miquel.raynal@bootlin.com