spi: dt-bindings: armada-3700: convert to dtschema

Convert txt binding of marvell armada 3700 SoC spi controller to dtschema
to allow for validation.

Signed-off-by: Kousik Sanagavarapu <five231003@gmail.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240417052729.6612-1-five231003@gmail.com


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