perf header: Rename "sibling cores" to "sibling sockets"

The "sibling cores" actually shows the sibling CPUs of a socket.  The
name "sibling cores" is very misleading.

Rename "sibling cores" to "sibling sockets"

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1559688644-106558-4-git-send-email-kan.liang@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>