dt-bindings: memory-controllers: add Samsung S5Pv210 SoC DMC

dt-bindings: memory-controllers: add Samsung S5Pv210 SoC DMC

Document bindings for the S5Pv210 SoC DMC memory controller, already
used in DTS and Linux CPU frequency scaling driver.  The binding looks
quite empty and is most likely incomplete, but the platform is so old
that no one expects any effort on this, except documenting what is in
DTS.

Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240312190348.724361-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>