perf vendor events arm64: Update scale units and descriptions of common topdown metrics

Metrics will be published here [1] going forwards, but they have
slightly different scale units. To allow autogenerated metrics to be
added more easily, update the scale units to match.

The more detailed descriptions have also been taken and added to the
common file.

[1]: https://gitlab.arm.com/telemetry-solution/telemetry-solution/-/tree/main/data/pmu/cpu/Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: James Clark <james.clark@arm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Nick Forrington <nick.forrington@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Sohom Datta <sohomdatta1@gmail.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20230811144017.491628-5-james.clark@arm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/pmu-events/arch/arm64/sbsa.json

 [
     {
-        "MetricExpr": "stall_slot_frontend / (#slots * cpu_cycles)",
-        "BriefDescription": "Frontend bound L1 topdown metric",
+        "MetricExpr": "100 * (stall_slot_frontend / (#slots * cpu_cycles))",
+        "BriefDescription": "This metric is the percentage of total slots that were stalled due to resource constraints in the frontend of the processor.",
         "DefaultMetricgroupName": "TopdownL1",
         "MetricGroup": "Default;TopdownL1",
         "MetricName": "frontend_bound",
-        "ScaleUnit": "100%"
+        "ScaleUnit": "1percent of slots"
     },
     {
-        "MetricExpr": "(1 - op_retired / op_spec) * (1 - stall_slot / (#slots * cpu_cycles))",
-        "BriefDescription": "Bad speculation L1 topdown metric",
+        "MetricExpr": "100 * ((1 - op_retired / op_spec) * (1 - stall_slot / (#slots * cpu_cycles)))",
+        "BriefDescription": "This metric is the percentage of total slots that executed operations and didn't retire due to a pipeline flush.\nThis indicates cycles that were utilized but inefficiently.",
         "DefaultMetricgroupName": "TopdownL1",
         "MetricGroup": "Default;TopdownL1",
         "MetricName": "bad_speculation",
-        "ScaleUnit": "100%"
+        "ScaleUnit": "1percent of slots"
     },
     {
-        "MetricExpr": "(op_retired / op_spec) * (1 - stall_slot / (#slots * cpu_cycles))",
-        "BriefDescription": "Retiring L1 topdown metric",
+        "MetricExpr": "100 * ((op_retired / op_spec) * (1 - stall_slot / (#slots * cpu_cycles)))",
+        "BriefDescription": "This metric is the percentage of total slots that retired operations, which indicates cycles that were utilized efficiently.",
         "DefaultMetricgroupName": "TopdownL1",
         "MetricGroup": "Default;TopdownL1",
         "MetricName": "retiring",
-        "ScaleUnit": "100%"
+        "ScaleUnit": "1percent of slots"
     },
     {
-        "MetricExpr": "stall_slot_backend / (#slots * cpu_cycles)",
-        "BriefDescription": "Backend Bound L1 topdown metric",
+        "MetricExpr": "100 * (stall_slot_backend / (#slots * cpu_cycles))",
+        "BriefDescription": "This metric is the percentage of total slots that were stalled due to resource constraints in the backend of the processor.",
         "DefaultMetricgroupName": "TopdownL1",
         "MetricGroup": "Default;TopdownL1",
         "MetricName": "backend_bound",
-        "ScaleUnit": "100%"
+        "ScaleUnit": "1percent of slots"
     }
 ]