tools/power/x86/intel_pstate_tracer: Add optional setting of trace buffer memory allocation

Allow the user to override the default trace buffer memory allocation
by adding a command line option to override the default.

The patch also:

Adds a SIGINT (i.e. CTRL C exit) handler,
so that things can be cleaned up before exit.

Moves the postion of some other cleanup from after to
before the potential "No valid data to plot" exit.

Replaces all quit() calls with sys.exit, because
quit() is not supposed to be used in scripts.

Signed-off-by: Doug Smythies <dsmythies@telus.net>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>