dt-bindings: soc: samsung: exynos-sysreg: add clocks for Exynos850

Exynos850 has dedicated clock for accessing SYSREGs.  Allow it, even
though Linux currently does not enable it and relies on bootloader.

Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20221127123259.20339-4-krzysztof.kozlowski@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>