perf symbols: Stop using map->groups, we can use kmaps instead

perf symbols: Stop using map->groups, we can use kmaps instead

To test that that function is being called I just added a probe on that
place, enabled it via 'perf trace' asking for at most 16 levels of
backtraces, system wide, and then ran 'perf top' on another xterm,
voilà:

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

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

  	perf record -e probe_perf:dso__process_kernel_symbol -aR sleep 1

  # perf trace -e probe_perf:dso__process_kernel_symbol/max-stack=16/ --max-events=2
  # perf trace -e probe_perf:dso__process_kernel_symbol/max-stack=16/ --max-events=2
       0.000 :17345/17345 probe_perf:dso__process_kernel_symbol(__probe_ip: 5680224)
                                         dso__process_kernel_symbol (/home/acme/bin/perf)
                                         dso__load_vmlinux (/home/acme/bin/perf)
                                         dso__load_vmlinux_path (/home/acme/bin/perf)
                                         dso__load (/home/acme/bin/perf)
                                         map__load (/home/acme/bin/perf)
                                         thread__find_map (/home/acme/bin/perf)
                                         machine__resolve (/home/acme/bin/perf)
                                         deliver_event (/home/acme/bin/perf)
                                         __ordered_events__flush.part.0 (/home/acme/bin/perf)
                                         process_thread (/home/acme/bin/perf)
                                         start_thread (/usr/lib64/libpthread-2.29.so)
       0.064 :17345/17345 probe_perf:dso__process_kernel_symbol(__probe_ip: 5680224)
                                         dso__process_kernel_symbol (/home/acme/bin/perf)
                                         dso__load_vmlinux (/home/acme/bin/perf)
                                         dso__load_vmlinux_path (/home/acme/bin/perf)
                                         dso__load (/home/acme/bin/perf)
                                         map__load (/home/acme/bin/perf)
                                         thread__find_map (/home/acme/bin/perf)
                                         machine__resolve (/home/acme/bin/perf)
                                         deliver_event (/home/acme/bin/perf)
                                         __ordered_events__flush.part.0 (/home/acme/bin/perf)
                                         process_thread (/home/acme/bin/perf)
                                         start_thread (/usr/lib64/libpthread-2.29.so)
  #
  # perf stat -e probe_perf:dso__process_kernel_symbol
  ^C
   Performance counter stats for 'system wide':

           107,308      probe_perf:dso__process_kernel_symbol

       8.215399813 seconds time elapsed
  #

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-5fy66x5hr5ct9pmw84jkiwvm@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>