When build_cpu_topo() encounters offline/absent CPUs, it fails to find any
sysfs entries and returns failure.

This leads to build_cpu_topology() and write_cpu_topology() failing as
well.

Because HEADER_CPU_TOPOLOGY has not been written, read leaves cpu_topology_map
NULL and we get NULL ptr deref at:

  ...
   cmd_test
    __cmd_test
     test_and_print
      run_test
       test_session_topology
        check_cpu_topology

  36: Session topology                           :
  --- start ---
  test child forked, pid 14902
  templ file: /tmp/perf-test-4CKocW
  failed to write feature HEADER_CPU_TOPOLOGY
  perf: Segmentation fault
  Obtained 9 stack frames.
  ./perf(sighandler_dump_stack+0x41) [0x5095f1]
  /lib64/libc.so.6(+0x35250) [0x7f4b7c3c9250]
  ./perf(test_session_topology+0x1db) [0x490ceb]
  ./perf() [0x475b68]
  ./perf(cmd_test+0x5b9) [0x4763c9]
  ./perf() [0x4945a3]
  ./perf(main+0x69f) [0x427e8f]
  /lib64/libc.so.6(__libc_start_main+0xf5) [0x7f4b7c3b5b35]
  ./perf() [0x427fb9]
  test child interrupted
  ---- end ----
  Session topology: FAILED!

This patch makes build_cpu_topology() skip offline/absent CPUs, by checking
their presence against cpu_map built from online CPUs.
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/a271b770175524f4961d4903af33798358a4a518.1487146877.git.jstancek@redhat.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>