spi: dt-bindings: airoha: Add YAML schema for SNFI controller

Introduce Airoha EN7581 SPI NAND controller binding

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Rajeev Kumar <Rajeev.Kumar@airoha.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://lore.kernel.org/r/f3377b323f00589e6b7ed7950c4840d18129238b.1714377864.git.lorenzo@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>