scripts/performance: Add topN_perf.py script

scripts/performance: Add topN_perf.py script

Syntax:
topN_perf.py [-h] [-n] <number of displayed top functions>  -- \
                 <qemu executable> [<qemu executable options>] \
                 <target executable> [<target execurable options>]

[-h] - Print the script arguments help message.
[-n] - Specify the number of top functions to print.
     - If this flag is not specified, the tool defaults to 25.

Example of usage:
topN_perf.py -n 20 -- qemu-arm coulomb_double-arm

Example Output:
 No.  Percentage  Name                       Invoked by
----  ----------  -------------------------  -------------------------
   1      16.25%  float64_mul                qemu-x86_64
   2      12.01%  float64_sub                qemu-x86_64
   3      11.99%  float64_add                qemu-x86_64
   4       5.69%  helper_mulsd               qemu-x86_64
   5       4.68%  helper_addsd               qemu-x86_64
   6       4.43%  helper_lookup_tb_ptr       qemu-x86_64
   7       4.28%  helper_subsd               qemu-x86_64
   8       2.71%  f64_compare                qemu-x86_64
   9       2.71%  helper_ucomisd             qemu-x86_64
  10       1.04%  helper_pand_xmm            qemu-x86_64
  11       0.71%  float64_div                qemu-x86_64
  12       0.63%  helper_pxor_xmm            qemu-x86_64
  13       0.50%  0x00007f7b7004ef95         [JIT] tid 491
  14       0.50%  0x00007f7b70044e83         [JIT] tid 491
  15       0.36%  helper_por_xmm             qemu-x86_64
  16       0.32%  helper_cc_compute_all      qemu-x86_64
  17       0.30%  0x00007f7b700433f0         [JIT] tid 491
  18       0.30%  float64_compare_quiet      qemu-x86_64
  19       0.27%  soft_f64_addsub            qemu-x86_64
  20       0.26%  round_to_int               qemu-x86_64

Signed-off-by: Ahmed Karaman <ahmedkhaledkaraman@gmail.com>
Signed-off-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Message-Id: <20200626164546.22102-2-ahmedkhaledkaraman@gmail.com>