system_power: Use PPU shutdown handlers
Created by: nicola-mazzucato-arm
System_power module uses drivers that are defined by the power_domain module. These drivers can optionally implement the shutdown function which is called during the shutdown procedure. This patch extends the shutdown procedure within this module so the shutdown function in the drivers will be called, if provided.
Change-Id: I8c02809ee5669f3651a19fa7b69a9c084521749e Signed-off-by: Nicola Mazzucato nicola.mazzucato@arm.com