perf metricgroup: Scale the metric result

Some metrics define the scale unit, such as

    {
        "BriefDescription": "Intel Optane DC persistent memory read latency (ns). Derived from unc_m_pmm_rpq_occupancy.all",
        "Counter": "0,1,2,3",
        "EventCode": "0xE0",
        "EventName": "UNC_M_PMM_READ_LATENCY",
        "MetricExpr": "UNC_M_PMM_RPQ_OCCUPANCY.ALL / UNC_M_PMM_RPQ_INSERTS / UNC_M_CLOCKTICKS",
        "MetricName": "UNC_M_PMM_READ_LATENCY",
        "PerPkg": "1",
        "ScaleUnit": "6000000000ns",
        "UMask": "0x1",
        "Unit": "iMC"
    },

For above example, the ratio should be,

ratio = (UNC_M_PMM_RPQ_OCCUPANCY.ALL / UNC_M_PMM_RPQ_INSERTS / UNC_M_CLOCKTICKS) * 6000000000

But in current code, the ratio is not scaled ( * 6000000000)

With this patch, the ratio is scaled and the unit (ns) is printed.

For example,
  #    219.4 ns  UNC_M_PMM_READ_LATENCY

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20190828055932.8269-4-yao.jin@linux.intel.com


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