dt-bindings: clock: gcc-sc8180x: Add the missing CX power domain

The GCC block is (mostly) powered by the VDD_CX rail. Allow specifying
it in power-domains.

Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231230-topic-8180_more_fixes-v1-1-93b5c107ed43@linaro.org


Signed-off-by: Bjorn Andersson <andersson@kernel.org>