These are the specific changes for ARM64 to make it possible to integrate the
DT based generic cpuidle driver in this tree.
It contains:
* The documentation for the DT definitions for ARM
* The refactoring of the cpu_suspend function for ARM64
* Introduce the cpu_idle_init function for ARM64
* Add the PSCI CPU SUSPEND based on the previous changes on cpu_suspend
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>