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

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 <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>