Add device bindings for cpuidle states for cpu devices.

Cc: devicetree@vger.kernel.orgi
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
Reviewed-by: Srinivas Rao L <lsrao@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/1586703004-13674-2-git-send-email-mkshah@codeaurora.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>