power_domain: Fix return status for notify_warm_reset

Created by: nicola-mazzucato-arm

notify_warm_reset returns false when notifications are not enabled, while it should return an integer and not a boolean.

Return FWK_SUCCESS when framework notifications are not available instead.

Change-Id: Ib2519e07e9dcd648a8b608c5bcc77d0a81986e57 Signed-off-by: Nicola Mazzucato nicola.mazzucato@arm.com