dt-bindings: mtd: partitions: Extend fixed-partitions binding

Extend fixed-partitions binding for support of Sercomm partition parser
(add "sercomm,sc-partitions" compatible).

Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220516151725.885427-1-csharper2005@gmail.com