perf util: Make the timechart SVG width dynamic

This patch adds a command line option for timechart that allows the
user to specify the width of the SVG file.

This patch also makes sure that each second of recording has at
least 200 units (pixels at 96 DPI) of width.  This impacts
recordings longer than 5 seconds; recordings shorter than 5 second
will scale up to have a width of 1000 units for the whole recording
(as before).

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20090920181416.69570c5d@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>