arm64: dts: qcom: msm8916: Use more generic idle state names

Instead of using Qualcomm-specific terminology, use generic node names
for the idle states that are easier to understand. Move the description
into the "idle-state-name" property.

Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Niklas Cassel <niklas.cassel@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>