perf hists: Support decaying in hierarchy mode

perf hists: Support decaying in hierarchy mode

In the hierarchy mode, hist entries should decay their children too.
Also update hists__delete_entry() to be able to free child entries.

Signed-off-by: Namhyung Kim <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>