dt_bindings: mtd: partitions: redboot: convert to YAML

Converts mtd/partitions/redboot-fis.txt to YAML.

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210628191440.2823024-1-clabbe@baylibre.com