dt-bindings: soc: renesas: Move renesas,rzg2l-sysc from arm to soc

The Renesas RZ/{G2L,V2L} System Controller (SYSC) DT binding is not
really a power-related DT binding, hence it does not belong under
Documentation/devicetree/bindings/power/.
Move it to Documentation/devicetree/bindings/soc/renesas/.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/a47015888f99476a5206a556dce93503494d9a73.1651495078.git.geert+renesas@glider.be