mem: Add callback to compute stats prior to dump event
The per rank statistics are periodically updated based on

state transition and refresh events.
Add a method to update these when a dump event occurs to

ensure they reflect accurate values.

Specifically, need to ensure that the low-power state

durations, power, and energy are logged correctly.
Change-Id: Ib642a6668340de8f494a608bb34982e58ba7f1eb

Reviewed-by: Radhika Jagtap <radhika.jagtap@arm.com>