spi: dt-bindings: Convert Synquacer SPI to DT schema

Convert the Socionext Synquacer SPI binding to DT format.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221209171644.3351787-1-robh@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>