[Perf pipe] Default initialize the maximum number of tasks

The maximum number of task pairs is now statically defined to
be 4 times the number of the CPU threads available on the target
machine. This allows to profile the system with up-to 8 tasks
per HW thread.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[Perf pipe] Plot a profiling output

Once a profiling has been completed, the generated ".dat" file is
directly plotted.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[Sched pipe] Plot PDF by default

By default a PDF plot is generated, unless the user pass the newly
added "show" command line flag.

Signed-off-by: Patrick Bellasi <derkling@gmail.com>
[Sched pipe] Cosmetics

Signed-off-by: Patrick Bellasi <derkling@gmail.com>