spi: spi-st-ssc: convert to DT schema

Convert spi-st-ssc.txt into st,ssc-spi.yaml for the
ST Microelectronics SSC SPI driver.

Signed-off-by: Alain Volmat <avolmat@me.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230213192349.17101-1-avolmat@me.com


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