arm64: dts: qcom: msm8996: Add PSCI cpuidle low power states

Add device bindings for cpuidle states for cpu devices.

msm8996 features 4 cpus - 2 in each cluster. However, all cpus implement
the same microarchitecture and the two clusters only differ in the
maximum frequency attainable by the CPUs.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <agross@kernel.org>