dt-bindings: mtd: atmel,dataflash: convert txt to yaml

Convert atmel-dataflash.txt into atmel,dataflash.yaml

Signed-off-by: Nayab Sayed <nayabbasha.sayed@microchip.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>