perf record: Export the callchain parsing routine and help

Will be used by perf top, that will first setup the symbol system to
deal with callchains and then call these routines to ask the kernel
for callchains.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
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/n/tip-jg0dh8rmlx7x11e7u7mnasvd@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>