perf callchain: Factor out adding new call chain entries

Move the code to resolve and add a new callchain entry into a new
add_callchain_ip function. This will be used in the next patches to add
LBRs too.

No change in behavior.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1415844328-4884-2-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>