feat(cactus): receive psci msg through direct req framework msg

Cactus receives PSCI CPU_OFF power management operation message
through framework direct request message and it will respond back
with framework direct message if all conditions are met.

Cactus SP1 and SP2 explicitly subscribe to CPU_OFF power management
message through their respective manifests.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I790a8698d238e29847e376b4fa9447a6241ef17e
7 files changed