perf symbols: Use kmaps(map)->machine when we know its a kernel map

And then stop using map->groups to achieve that.

To test that that branch is being taken, probe the function that is only
called from there and then run something like 'perf top' in another
xterm:

  # perf probe -x ~/bin/perf machine__map_x86_64_entry_trampolines
  Added new event:
    probe_perf:machine__map_x86_64_entry_trampolines (on machine__map_x86_64_entry_trampolines in /home/acme/bin/perf)

  You can now use it in all perf tools, such as:

  	perf record -e probe_perf:machine__map_x86_64_entry_trampolines -aR sleep 1

  # perf trace -e probe_perf:*
       0.000 bash/10614 probe_perf:machine__map_x86_64_entry_trampolines(__probe_ip: 5224944)
  ^C#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-lgrrzdxo2p9liq2keivcg887@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>