spi: dt-bindings: samsung: Add Exynos4210 SPI

Document samsung,exynos4210-spi compatible which is already used on
several Exynos SoCs.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Chanho Park <chanho61.park@samsung.com>
Link: https://lore.kernel.org/r/20220626112838.19281-1-krzysztof.kozlowski@linaro.org


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