perf tools: Provide help for subset of options

Some tools have a lot of options, so, providing a way to show help just
for some of them may come handy:

  $ perf report -h --tui

   Usage: perf report [<options>]

        --tui             Use the TUI interface

  $ perf report -h --tui --showcpuutilization -b -c

   Usage: perf report [<options>]

    -b, --branch-stack    use branch records for per branch histogram filling
    -c, --comms <comm[,comm...]>
                          only consider symbols in these comms
        --showcpuutilization
                          Show sample percentage for different cpu modes
        --tui             Use the TUI interface

  $

Using it with perf bash completion is also handy, just make sure you
source the needed file:

  $ . ~/git/linux/tools/perf/perf-completion.sh

Then press tab/tab after -- to see a list of options, put them after -h
and only the options chosen will have its help presented:

  $ perf report -h --
  --asm-raw              --demangle-kernel      --group
  --kallsyms             --pretty               --stdio
  --branch-history       --disassembler-style   --gtk
  --max-stack            --showcpuutilization   --symbol-filter
  --branch-stack         --dsos                 --header
  --mem-mode             --show-info            --symbols
  --call-graph           --dump-raw-trace       --header-only
  --modules              --show-nr-samples      --symfs
  --children             --exclude-other        --hide-unresolved
  --objdump              --show-ref-call-graph  --threads
  --column-widths        --fields               --ignore-callees
  --parent               --show-total-period    --tid
  --comms                --field-separator      --input
  --percentage           --socket-filter        --tui
  --cpu                  --force                --inverted
  --percent-limit        --sort                 --verbose
  --demangle             --full-source-path     --itrace
  --pid                  --source               --vmlinux
  $ perf report -h --socket-filter

   Usage: perf report [<options>]

      --socket-filter <n>
                  only show processor socket that match with this filter

Suggested-by: Ingo Molnar <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brendan Gregg <[email protected]>
Cc: Chandler Carruth <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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