perf sort: Separate out branch stack specific sort keys

Current perf report gets segmentation fault when a branch stack specific
sort key is provided by --sort option to a perf.data file which contains
no branch infomation.  It's because those sort keys reference branch
info of a hist entry unconditionally.  Maybe we can change it checks
whether such branch info is valid or not.  But if the branch stacks are
not recorded, it'd be nop.  Thus it'd be better to make those keys are
unselectable.

This patch separates those keys to a different dimension array, so that
if user passes such a key to a file which has no branch stack will get
following message rather than a segfault.

  Error: Invalid --sort key: `symbol_from'

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reported-by: Stefan Beller <stefanbeller@googlemail.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1356599507-14226-10-git-send-email-namhyung@kernel.org


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