perf metricgroup: Make find_metric() public with name change

perf metricgroup: Make find_metric() public with name change

Function find_metric() is required for the metric processing in the
pmu-events testcase, so make it public. Also change the name to include
"metricgroup".

Tested-by: Paul A. Clarke <pc@us.ibm.com>
Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will@kernel.org>
Cc: linuxarm@huawei.com
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/1617791570-165223-2-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>