dt-bindings: mtd: qcom,nandc: Define properties at top-level

Convention is DT schemas should define all properties at the top-level
and not inside of if/then schemas. That minimizes the if/then schemas
and is more future proof.

There were 2 "if" schemas for "qcom,ipq806x-nand" and the
"qcom,boot-partitions: true" unnecessary, so the conditional schemas
can be simplified a bit.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240625215605.192260-1-robh@kernel.org