dt-bindings: mtd: qcom: Fix a property position

qcom,boot-partitions is a NAND chip property, not a NAND controller
property. Move the description of the property into the NAND chip
section and just enable the property in the if/else block.

Fixes: 5278cc93

 ("dt-bindings: mtd: qcom_nandc: document qcom,boot-partitions binding")
Cc: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/linux-mtd/20230619092916.3028470-6-miquel.raynal@bootlin.com