perf hists: Introduce hists__scnprint_title()

That is not use any struct hists_browser internals, so that it can be
shared with the other UIs and tools.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin Liška <mliska@suse.cz>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196935
Link: https://lkml.kernel.org/n/tip-w8mczjnqnbcj9yzfkv9ja6ro@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>