feat(psci): add a helper function to ensure that non-boot PEs are offline

Introduce a helper function that ensures that non-boot PEs are offline.
This function will be used by DRTM implementation to ensure that system
is running with only single PE.

Signed-off-by: Manish V Badarkhe <manish.badarkhe@arm.com>
Signed-off-by: Lucian Paul-Trifu <lucian.paultrifu@gmail.com>
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I521ebefa49297026b02554629b1710a232148e01
3 files changed