arm64: dts: qcom: sc8180x: Add missing CPU off state

The CPUs can be powered off without pulling the plug from the rest of
the system. Describe the idle state responsible for this.

Fixes: 8575f197 ("arm64: dts: qcom: Introduce the SC8180x platform")
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20231230-topic-8180_more_fixes-v1-4-93b5c107ed43@linaro.org


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