perf callchain: Move callchain specific routines from util.[ch]

Where they belong, no point in leaving those in the generic "util"
files.

Link: http://lkml.kernel.org/n/tip-ljx3iiip1hlfa7a7apjem7ph@git.kernel.org


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