analysis/tasks: add support for custom signals
analysis/tasks: add support for custom signals

The plotTasks() function is currently limited to a predefined set of
signals which are generated in different plots. Out of these plots, the
first one in quite convenient to represent other custom signals which are
eventually present in the trace_sched_load_avg DF.

Teach plotTasks() how to plot additional custom signals if they are present
as valid columns in the trace_sched_load_avg DF.

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

ARM-software/lisa,credp/lisa,ARM-software/lisa,arnoldlu/lisa,bjackman/lisa,credp/lisa,ARM-software/lisa,credp/lisa,mdigiorgio/lisa,joelagnel/lisa,mdigiorgio/lisa,bjackman/lisa,ARM-software/lisa,arnoldlu/lisa,credp/lisa,joelagnel/lisa