juno: Fix juno_system notification handler
The Juno System module is currently returning FWK_E_PARAM from its notification handler in cases where it should be returning FWK_SUCCESS. This commit fixes this issue and simplifies the notification handling logic.
Change-Id: If50906186603f6f119f9c18687ef664947ebf0b4 Signed-off-by: Chris Kay chris.kay@arm.com