spi: atmel,quadspi: Convert to json-schema

Convert the Atmel QuadSPI controller Device Tree binding documentation
to json-schema.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211209122939.339810-2-tudor.ambarus@microchip.com


Signed-off-by: Mark Brown <broonie@kernel.org>