utils/trace: using a single DataFrame to report both PIDs and task names
utils/trace: using a single DataFrame to report both PIDs and task names

Currently we are building to dataftames to index tasks by PIDs and Name which
can be accomplished more efficiently using a single DF.

This patch removes the _tasks_by_name DF and updates the two getter functions:
  getTaskByName
  getTaskByPid
to better use the remaining _tasks_by_pid DF.

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

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