libs/utils/trace: avoid interleaved cpu_frequency events between devl…

Created by: mdigiorgio

devlib injects fake cpu_frequency events at the beginning of a trace to get information about the frequency. However, in some cases those events get mixed with real cpu_frequency trace events generated by the cpufreq governor. This leads to getting a dataframe with with wrong events and also makes the cluster frequency coherency checks fail, whereas they should not.

For this reason, LISA checks whether the fake events for all CPUs happen before the first event generated by the cpufreq governor and if this is the case they are inserted as first events in the cpu_frequency dataframe.

Signed-off-by: Michele Di Giorgio michele.digiorgio@arm.com