perf hists browser: Zoom in/out for processor socket

Currently, users can zoom in/out for threads and dso in 'perf top' and
'perf report'.

This patch extends it for the processor sockets.

'S' is the short key to zoom into current Processor Socket.

Signed-off-by: Kan Liang <kan.liang@intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1441377946-44429-4-git-send-email-kan.liang@intel.com


[ - Made it elide the Socket column when zooming into it,
    just like with the other zoom ops;
  - Make it use browser->pstack, to unzoom level by level;
  - Rename 'socket' variables to 'socket_id' to make it build on
    older systems where it shadows a global glibc declaration ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>