stats: Add first_cpu aggregator function
stats: Add first_cpu aggregator function

The first_cpu function can be used to find out the first
cpu on which the task ran on across the topology

Change-Id: I5dbed1291bf6aef7f8bceada8aa73db11a96e0ec
Signed-off-by: Kapileshwar Singh <d373e2b6407ea84be359ce4a11e8631121819e79@arm.com>

sinkap/trappy,sinkap/trappy,bjackman/trappy,joelagnel/trappy,joelagnel/trappy,bjackman/trappy,bjackman/trappy,derkling/trappy,JaviMerino/trappy,ARM-software/trappy,bjackman/trappy,sinkap/trappy,ARM-software/trappy,derkling/trappy,joelagnel/trappy,JaviMerino/trappy,sinkap/trappy,ARM-software/trappy,ARM-software/trappy,derkling/trappy,JaviMerino/trappy,joelagnel/trappy