perf/core improvements:

User visible:

- Hierarchy histogram mode for 'perf top' and 'perf report', showing multiple
  levels, one per --sort entry: (Namhyung Kim)

  On a mostly idle system:

  # perf top --hierarchy -s comm,dso

  Then expand some levels and use 'P' to take a snapshot:

  # cat perf.hist.0
  -  92.32%         perf
        58.20%         perf
        22.29%         libc-2.22.so
         5.97%         [kernel]
         4.18%         libelf-0.165.so
         1.69%         [unknown]
  -   4.71%         qemu-system-x86
         3.10%         [kernel]
         1.60%         qemu-system-x86_64 (deleted)
  +   2.97%         swapper
  #

- Check availability of memory events in 'perf mem': (Jiri Olsa)

  On a Intel Broadwell machine:

  # perf mem record -e list
  ldlat-loads : available
  ldlat-stores: available
  #

- Decode data_src values (e.g. perf.data files generated by 'perf mem record')
  in 'perf script': (Jiri Olsa)

  # perf script
    perf 693 [1] 4.088652: 1 cpu/mem-loads,ldlat=30/P: ffff88007d0b0f40 68100142 L1 hit|SNP None|TLB L1 or L2 hit|LCK No <SNIP>
                                                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- Print bpf-output events in 'perf script': (Wang Nan).

  # perf record -e bpf-output/no-inherit,name=evt/ -e ./test_bpf_output_3.c/map:channel.event=evt/ usleep 1000
  # perf script
     usleep  4882 21384.532523:   evt:  ffffffff810e97d1 sys_nanosleep ([kernel.kallsyms])
      BPF output: 0000: 52 61 69 73 65 20 61 20  Raise a
                  0008: 42 50 46 20 65 76 65 6e  BPF even
                  0010: 74 21 00 00              t!..
      BPF string: "Raise a BPF event!"
  #

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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