perf symbols: Treat all memory maps without dso file as loaded

The stack/vdso/heap memory maps dont have any dso file.  Setting the
perf dso objects as 'loaded' for these maps, we avoid unnecessary
warnings like:

  "Failed to open [stack], continuing without symbols"

All map__find_* functions still return NULL when searching for symbols
in these maps.

Link: http://lkml.kernel.org/r/20110824131834.GA2007@jolsa.brq.redhat.com


Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>