perf timechart: Add a process filter

During the Kernel Summit demo of perf/ftrace/timechart, there
was a feature request to have a process filter for timechart so
that you can zoom into one or a few processes that you are
really interested in.

This patch adds basic support for this feature, the -p
(--process) option now can select a PID or a process name to be
shown. Multiple -p options are allowed, and the combined set
will be included in the output.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20091020070939.7d0fb8a7@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>