Both Cortex-Ares and Cortex-A76 CPUs use the ARM DynamIQ Shared Unit
(DSU).  The power-down and power-up sequences are therefore mostly
managed in hardware, and required software operations are simple.

Change-Id: I3a9447b5bdbdbc5ed845b20f6564d086516fa161
Signed-off-by: Isla Mitchell <isla.mitchell@arm.com>