perf symbols: Mark if a symbol is idle in the library

This was being done just in 'perf top', but grouping idle symbols should
be useful in other places as well, so remove one more symbol_filter_t
user by moving this to the symbol library.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-5r7xitjkzjr9jak1zy3d8u5l@git.kernel.org


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