tasks_analysis: Add a multiple-tasks CPUs residency plot

Created by: derkling

This provides a new convenient task analysis API to generate a stacked plot of CPUs residency time for a list of specified tasks.

Such an analysis could be useful to identify where a bunch of important tasks (e.g. top-app tasks) spend most of their time. The generated dataframe and plots sorts tasks by increasing running time, thus making it even more simple to identify the most active tasks.

Signed-off-by: Patrick Bellasi patrick.bellasi@arm.com