mtd: parsers: ofpart: add workaround for #size-cells 0

Add a mechanism to handle the case in which partitions are present as
direct child of the nand controller node and #size-cells is set to <0>.

This could happen if the nand-controller node in the DTS is supposed to
have #size-cells set to 0, but for some historical reason/bug it was set
to 1 in the past, and the firmware (e.g. U-Boot) is adding the partition
as direct children of the nand-controller defaulting to #size-cells
being to 1.

This prevents a real boot failure on colibri-imx7 that happened during v6.1
development cycles.

Link: https://lore.kernel.org/all/Y4dgBTGNWpM6SQXI@francesco-nb.int.toradex.com/
Link: https://lore.kernel.org/all/20221202071900.1143950-1-francesco@dolcini.it/


Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230124104444.330913-1-francesco@dolcini.it