perf hists browser: Support folded callchains

perf hists browser: Support folded callchains

The folded callchain mode prints all chains in a single line.

Currently perf report --tui doesn't support folded callchains.  Like
flat callchains, only leaf nodes are added to the final rbtree so it
should show entries in parent nodes.  To do that, add flat_val list to
struct callchain_node and show them along with the (normal) val list.

For example, folded callchain looks like below:

  $ perf report -g folded --tui
  Samples: 234  of event 'cycles:pp', Event count (approx.): 32605268
    Overhead  Command  Shared Object     Symbol
  -   39.93%  swapper  [kernel.vmlinux]  [k] intel_idle
     + 28.63% intel_idle; cpuidle_enter_state; cpuidle_enter; ...
     + 11.30% intel_idle; cpuidle_enter_state; cpuidle_enter; ...

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1447047946-1691-9-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>