lisa.analysis.latency: Include CPUs in latency DFs
Created by: mrkajetanp
Latency-related functions such as df_latency_wakeup and df_latency_preemption at the moment do not return any information about which CPUs the latency ocurred on.
Add a 'cpu' column to df_latency_preemption along with 'cpu' & 'target_cpu' columns to df_latency_wakeup.