We need to initializa some fields (right now just a mutex) when we
allocate the per symbol annotation struct, so do it at the symbol
constructor instead of (ab)using the filter mechanism for that.

This way we remove one of the few cases we have for that symbol filter,
which will eventually led to removing it.

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: http://lkml.kernel.org/n/tip-cvz34avlz1lez888lob95390@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>