[TF-A] PSCI OS-initiated mode

Hi,

The PSCI specification defines two different power state coordination modes for CPU_SUSPEND that can be used to put a core or a group of cores into a low-power state. These modes are the platform-coordinated mode (default) and the OS-initiated mode (optional). OS-initiated mode is currently not supported by TF-A, while both modes are supported by the Linux Kernel.

Requesting reviews for the patches [1] adding support for OS-initiated mode in TF-A and the corresponding tests in TF-A-Tests. Any feedback and comments are much appreciated.

Thanks in advance!

Wing

[1] https://review.trustedfirmware.org/q/topic:psci-osi