perf annotate: Allow disassembly using /proc/kcore

perf annotate: Allow disassembly using /proc/kcore

Annotation with /proc/kcore is possible so the logic is adjusted to
allow it.  The main difference is that /proc/kcore had no symbols so the
parsing logic needed a tweak to read jump offsets.

The other difference is that objdump cannot always read from kcore.
That seems to be a bug with objdump.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1375875537-4509-11-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>