cpu: Add frequency scaling to the Trace CPU

cpu: Add frequency scaling to the Trace CPU

This change adds a simple feature to scale the frequency of
the Trace CPU.

The compute delays in the input traces provide timing. This
change adds a freqency multiplier parameter to the Trace CPU
set to 1.0 by default. The compute delay is manipulated to
effectively achieve the  frequency at which the nodes become
ready and thus scale the frequency of the Trace CPU.

Change-Id: Iaabbd57806941ad56094fcddbeb38fcee1172431
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>