This patch defines and registers the SPMD PM handler hooks.
This is intended to relay boot and PM events to the SPMC.

Change-Id: If5a758d22b8d2152cbbb83a0cad563b5e1c6bd49
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>