latency_analysis: add statistics getter method

Created by: derkling

Right now, the plotLatency method returns a DF with statistics for the latencies of a specified task. However, sometimes we could be interested in getting these stats without necessarily plotting all the data.

Let's move the statistics DF generation into an internal _get_latency_df method, which can then be used by the plotLatency but also from an additional DF gatter: _dfg_latency_stats_df. Thus, this will make available a new:

trace.data_frame.latency_stats_df()

which just return the overall latency stats for the specified task.

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