dt-bindings: mfd: mediatek: Add scpsys compatible for mt8186

Add a new scpsys compatible for mt8186 SoC.

Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220923131148.6678-2-allen-kh.cheng@mediatek.com