perf hists: Introduce hist_entry__has_callchain() method

perf hists: Introduce hist_entry__has_callchain() method

We'll use this helper more frequently when reworking
symbol_conf.use_callchain logic, where knowing if a hist_entry has
callchains is the important bit, so make going from hist_entry to hists
to evsel easier, compact.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-p6gioxkzpkpz71dtt4wcs36o@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>