perf c2c: Display "Total Stores" as a standalone metrics

The total stores is displayed under the metrics "Store Reference", to
output the same format with total records and all loads, extract the
total stores number as a standalone metrics "Total Stores".

After this patch, the tool shows the summary numbers ("Total records",
"Total loads", "Total Stores") in the unified form.

Before:

  #        ----------- Cacheline ----------      Tot  ----- LLC Load Hitm -----    Total    Total  ---- Store Reference ----  --- Load Dram ----      LLC  ----- Core Load Hit -----  -- LLC Load Hit --
  # Index             Address  Node  PA cnt     Hitm    Total      Lcl      Rmt  records    Loads    Total    L1Hit   L1Miss       Lcl       Rmt  Ld Miss       FB       L1       L2       Llc       Rmt
  # .....  ..................  ....  ......  .......  .......  .......  .......  .......  .......  .......  .......  .......  ........  ........  .......  .......  .......  .......  ........  ........
  #
        0      0x55f07d580100     0    1499   85.89%      481      481        0     7243     3879     3364     2599      765         0         0        0      548     2615       66       169         0
        1      0x55f07d580080     0       1   13.93%       78       78        0      664      664        0        0        0         0         0        0      187      361       27        11         0
        2      0x55f07d5800c0     0       1    0.18%        1        1        0      405      405        0        0        0         0         0        0      131        0       10       263         0

After:

  #        ----------- Cacheline ----------      Tot  ----- LLC Load Hitm -----    Total    Total    Total  ---- Stores ----  --- Load Dram ----      LLC  ----- Core Load Hit -----  -- LLC Load Hit --
  # Index             Address  Node  PA cnt     Hitm    Total      Lcl      Rmt  records    Loads   Stores    L1Hit   L1Miss       Lcl       Rmt  Ld Miss       FB       L1       L2       Llc       Rmt
  # .....  ..................  ....  ......  .......  .......  .......  .......  .......  .......  .......  .......  .......  ........  ........  .......  .......  .......  .......  ........  ........
  #
        0      0x55f07d580100     0    1499   85.89%      481      481        0     7243     3879     3364     2599      765         0         0        0      548     2615       66       169         0
        1      0x55f07d580080     0       1   13.93%       78       78        0      664      664        0        0        0         0         0        0      187      361       27        11         0
        2      0x55f07d5800c0     0       1    0.18%        1        1        0      405      405        0        0        0         0         0        0      131        0       10       263         0

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Joe Mario <jmario@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201014050921.5591-3-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>