perf timechart: Introduce tool struct

perf timechart: Introduce tool struct

To avoid having all those global variables and to use the interface to
event processing that is based on passing a 'perf_tool' struct that
should be embedded in a per tool specific struct passed to all the
sample processing callbacks.

There are some more globals to move, next patches will do it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stanislav Fomichev <stfomichev@yandex-team.ru>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-0iah65pq796ezbk5u1lzwy1k@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>